Oracle database 12c sql worshop 2 student guide vol 1

Oracle Database 12c: SQL
Workshop II
Student Guide - Volume I
D80194GC10
Edition 1.0
August 2013
D83185
OracleUniversityandEgabiSolutionsuseonly
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Author
Dimpi Rani Sarmah
Technical Contributors
and Reviewers
Nancy Greenberg
Swarnapriya Shridhar
Bryan Roberts,
Laszlo Czinkoczki
KimSeong Loh
Brent Dayley
Jim Spiller
Christopher Wensley
Maheshwari Krishnamurthy
Daniel Milne
Michael Almeida
Diganta Choudhury
Anjulaponni Azhagulekshmi
Subbiahpillai
Manish Pawar
Clair Bennett
Yanti Chang
Joel Goodman
Gerlinde Frenzen
Publisher
Sujatha Nagendra

iii
Contents
1 Introduction
Lesson Objectives 1-2
Lesson Agenda 1-3
Course Objectives 1-4
Course Prerequisites 1-5
Course Agenda 1-6
Lesson Agenda 1-7
Tables Used in This Course 1-8
Appendixes and Practices Used in This Course 1-10
Development Environments 1-11
Lesson Agenda 1-12
Review of Restricting Data 1-13
Review of Sorting Data 1-14
Review of SQL Functions 1-15
Review of Single-Row Functions 1-16
Review of Types of Group Functions 1-17
Review of Using Subqueries 1-18
Review of Managing Tables Using DML Statements 1-20
Lesson Agenda 1-22
Oracle Database SQL Documentation 1-23
Additional Resources 1-24
Summary 1-25
Practice 1: Overview 1-26
2 Introduction to Data Dictionary Views
Objectives 2-2
Lesson Agenda 2-3
Data Dictionary 2-4
Data Dictionary Structure 2-5
How to Use the Dictionary Views 2-7
USER_OBJECTS and ALL_OBJECTS Views 2-8
USER_OBJECTS View 2-9
Lesson Agenda 2-10
Table Information 2-11
Column Information 2-12

iv
Constraint Information 2-14
USER_CONSTRAINTS: Example 2-15
Querying USER_CONS_COLUMNS 2-16
Lesson Agenda 2-17
Adding Comments to a Table 2-18
Quiz 2-19
Summary 2-20
3 Creating Sequences, Synonyms, and Indexes
Objectives 3-2
Lesson Agenda 3-3
Database Objects 3-4
Referencing Another User’s Tables 3-5
Sequences 3-6
CREATE SEQUENCE Statement: Syntax 3-7
Creating a Sequence 3-9
NEXTVAL and CURRVAL Pseudocolumns 3-10
Using a Sequence 3-12
SQL Column defaulting using a Sequence 3-13
Caching Sequence Values 3-14
Modifying a Sequence 3-15
Guidelines for Modifying a Sequence 3-16
Sequence Information 3-17
Lesson Agenda 3-18
Synonyms 3-19
Creating a Synonym for an Object 3-20
Creating and Removing Synonyms 3-21
Synonym Information 3-22
Lesson Agenda 3-23
Indexes 3-24
How Are Indexes Created? 3-25
Creating an Index 3-26
CREATE INDEX with the CREATE TABLE Statement 3-27
Function-Based Indexes 3-29
Creating Multiple Indexes on the Same Set of Columns 3-30
Example of Creating Multiple Indexes on the Same Set Of Columns 3-31
Index Creation Guidelines 3-32
Index Information 3-33
USER_INDEXES: Examples 3-34
Querying USER_IND_COLUMNS 3-35

v
Removing an Index 3-36
Quiz 3-37
Summary 3-38
4 Creating Views
Objectives 4-2
Lesson Agenda 4-3
Database Objects 4-4
What Is a View? 4-5
Advantages of Views 4-6
Simple Views and Complex Views 4-7
Creating a View 4-8
Retrieving Data from a View 4-11
Modifying a View 4-12
Creating a Complex View 4-13
View Information 4-14
Rules for Performing DML Operations on a View 4-15
Using the WITH CHECK OPTION Clause 4-18
Denying DML Operations 4-19
Removing a View 4-21
Quiz 4-22
Summary 4-23
5 Managing Schema Objects
Objectives 5-2
Lesson Agenda 5-3
Adding a Constraint Syntax 5-4
Adding a Constraint 5-5
Dropping a Constraint 5-6
Dropping a CONSTRAINT ONLINE 5-7
ON DELETE Clause 5-8
Cascading Constraints 5-9
Renaming Table Columns and Constraints 5-12
Disabling Constraints 5-13
Enabling Constraints 5-14
Deferring Constraints 5-15
Difference Between INITIALLY DEFERRED and INITIALLY IMMEDIATE 5-16
DROP TABLE … PURGE 5-18
Lesson Agenda 5-19

vi
Temporary Tables 5-20
Creating a Temporary Table 5-21
Lesson Agenda 5-22
External Tables 5-23
Creating a Directory for the External Table 5-24
Creating an External Table 5-26
Creating an External Table by Using ORACLE_LOADER 5-28
Querying External Tables 5-30
Creating an External Table by Using ORACLE_DATAPUMP: Example 5-31
Quiz 5-32
Summary 5-33
6 Retrieving Data by Using Subqueries
Objectives 6-2
Lesson Agenda 6-3
Retrieving Data by Using a Subquery as a Source 6-4
Lesson Agenda 6-6
Multiple-Column Subqueries 6-7
Column Comparisons 6-8
Pairwise Comparison Subquery 6-9
Nonpairwise Comparison Subquery 6-11
Lesson Agenda 6-13
Scalar Subquery Expressions 6-14
Scalar Subqueries: Examples 6-15
Lesson Agenda 6-17
Correlated Subqueries 6-18
Using Correlated Subqueries 6-20
Lesson Agenda 6-22
Using the EXISTS Operator 6-23
Find All Departments That Do Not Have Any Employees 6-25
Lesson Agenda 6-26
WITH Clause 6-27
WITH Clause: Example 6-28
Recursive WITH Clause 6-30
Recursive WITH Clause: Example 6-31
Quiz 6-32
Summary 6-33

vii
7 Manipulating Data by Using Subqueries
Objectives 7-2
Lesson Agenda 7-3
Using Subqueries to Manipulate Data 7-4
Lesson Agenda 7-5
Inserting by Using a Subquery as a Target 7-6
Lesson Agenda 7-8
Using the WITH CHECK OPTION Keyword on DML Statements 7-9
Lesson Agenda 7-11
Correlated UPDATE 7-12
Using Correlated UPDATE 7-13
Correlated DELETE 7-15
Using Correlated DELETE 7-16
Summary 7-17
8 Controlling User Access
Objectives 8-2
Lesson Agenda 8-3
Controlling User Access 8-4
Privileges 8-5
System Privileges 8-6
Creating Users 8-7
User System Privileges 8-8
Granting System Privileges 8-10
Lesson Agenda 8-11
What Is a Role? 8-12
Creating and Granting Privileges to a Role 8-13
Changing Your Password 8-14
Lesson Agenda 8-15
Object Privileges 8-16
Granting Object Privileges 8-18
Passing On Your Privileges 8-19
Confirming Granted Privileges 8-20
Lesson Agenda 8-21
Revoking Object Privileges 8-22
Quiz 8-24
Summary 8-25

viii
9 Manipulating Data
Objectives 9-2
Lesson Agenda 9-3
Explicit Default Feature: Overview 9-4
Using Explicit Default Values 9-5
Copying Rows from Another Table 9-6
Lesson Agenda 9-7
Multitable INSERT Statements: Overview 9-8
Types of Multitable INSERT Statements 9-10
Multitable INSERT Statements 9-11
Unconditional INSERT ALL 9-13
Conditional INSERT ALL: Example 9-15
Conditional INSERT ALL 9-16
Conditional INSERT FIRST: Example 9-18
Conditional INSERT FIRST 9-19
Pivoting INSERT 9-21
Lesson Agenda 9-24
MERGE Statement 9-25
MERGE Statement Syntax 9-26
Merging Rows: Example 9-27
Lesson Agenda 9-30
FLASHBACK TABLE Statement 9-31
Using the FLASHBACK TABLE Statement 9-33
Lesson Agenda 9-34
Tracking Changes in Data 9-35
Flashback Version Query: Example 9-36
VERSIONS BETWEEN Clause 9-37
Quiz 9-38
Summary 9-40
10 Managing Data in Different Time Zones
Objectives 10-2
Lesson Agenda 10-3
Time Zones 10-4
TIME_ZONE Session Parameter 10-5
CURRENT_DATE, CURRENT_TIMESTAMP, and LOCALTIMESTAMP 10-6
Comparing Date and Time in a Session’s Time Zone 10-7
DBTIMEZONE and SESSIONTIMEZONE 10-9
TIMESTAMP Data Types 10-10
TIMESTAMP Fields 10-11

ix
Difference Between DATE and TIMESTAMP 10-12
Comparing TIMESTAMP Data Types 10-13
Lesson Agenda 10-14
INTERVAL Data Types 10-15
INTERVAL Fields 10-17
INTERVAL YEAR TO MONTH: Example 10-18
INTERVAL DAY TO SECOND Data Type: Example 10-20
Lesson Agenda 10-21
EXTRACT 10-22
TZ_OFFSET 10-23
FROM_TZ 10-25
TO_TIMESTAMP 10-26
TO_YMINTERVAL 10-27
TO_DSINTERVAL 10-28
Daylight Saving Time (DST) 10-29
Quiz 10-31
Summary 10-32
A Table Descriptions
B Using SQL Developer
Objectives B-2
What Is Oracle SQL Developer? B-3
Specifications of SQL Developer B-4
SQL Developer 3.2 Interface B-5
Creating a Database Connection B-7
Browsing Database Objects B-10
Displaying the Table Structure B-11
Browsing Files B-12
Creating a Schema Object B-13
Creating a New Table: Example B-14
Using the SQL Worksheet B-15
Executing SQL Statements B-19
Saving SQL Scripts B-20
Executing Saved Script Files: Method 1 B-21
Executing Saved Script Files: Method 2 B-22
Formatting the SQL Code B-23
Using Snippets B-24
Using Snippets: Example B-25
Using Recycle Bin B-26

x
Debugging Procedures and Functions B-27
Database Reporting B-28
Creating a User-Defined Report B-29
Search Engines and External Tools B-30
Setting Preferences B-31
Resetting the SQL Developer Layout B-33
Data Modeler in SQL Developer B-34
Summary B-35
C Using SQL*Plus
Objectives C-2
SQL and SQL*Plus Interaction C-3
SQL Statements Versus SQL*Plus Commands C-4
Overview of SQL*Plus C-5
Logging In to SQL*Plus C-6
Displaying the Table Structure C-7
SQL*Plus Editing Commands C-9
Using LIST, n, and APPEND C-11
Using the CHANGE Command C-12
SQL*Plus File Commands C-13
Using the SAVE, START Commands C-14
SERVEROUTPUT Command C-15
Using the SQL*Plus SPOOL Command C-16
Using the AUTOTRACE Command C-17
Summary C-18
D Commonly Used SQL Commands
Objectives D-2
Basic SELECT Statement D-3
SELECT Statement D-4
WHERE Clause D-5
ORDER BY Clause D-6
GROUP BY Clause D-7
Data Definition Language D-8
CREATE TABLE Statement D-9
ALTER TABLE Statement D-10
DROP TABLE Statement D-11
GRANT Statement D-12
Privilege Types D-13
REVOKE Statement D-14
TRUNCATE TABLE Statement D-15

xi
Data Manipulation Language D-16
INSERT Statement D-17
UPDATE Statement Syntax D-18
DELETE Statement D-19
Transaction Control Statements D-20
COMMIT Statement D-21
ROLLBACK Statement D-22
SAVEPOINT Statement D-23
Joins D-24
Types of Joins D-25
Qualifying Ambiguous Column Names D-26
Natural Join D-27
Equijoins D-28
Retrieving Records with Equijoins D-29
Additional Search Conditions Using the AND and WHERE Operators D-30
Retrieving Records with Nonequijoins D-31
Retrieving Records by Using the USING Clause D-32
Retrieving Records by Using the ON Clause D-33
Left Outer Join D-34
Right Outer Join D-35
Full Outer Join D-36
Self-Join: Example D-37
Cross Join D-38
Summary D-39
E Generating Reports by Grouping Related Data
Objectives E-2
Review of Group Functions E-3
Review of the GROUP BY Clause E-4
Review of the HAVING Clause E-5
GROUP BY with ROLLUP and CUBE Operators E-6
ROLLUP Operator E-7
ROLLUP Operator: Example E-8
CUBE Operator E-9
CUBE Operator: Example E-10
GROUPING Function E-11
GROUPING Function: Example E-12
GROUPING SETS E-13
GROUPING SETS: Example E-15
Composite Columns E-17
Composite Columns: Example E-19

xii
Concatenated Groupings E-21
Concatenated Groupings: Example E-22
Summary E-23
F Hierarchical Retrieval
Objectives F-2
Sample Data from the EMPLOYEES Table F-3
Natural Tree Structure F-4
Hierarchical Queries F-5
Walking the Tree F-6
Walking the Tree: From the Bottom Up F-8
Walking the Tree: From the Top Down F-9
Ranking Rows with the LEVEL Pseudocolumn F-10
Formatting Hierarchical Reports Using LEVEL and LPAD F-11
Pruning Branches F-13
Summary F-14
G Writing Advanced Scripts
Objectives G-2
Using SQL to Generate SQL G-3
Creating a Basic Script G-4
Controlling the Environment G-5
The Complete Picture G-6
Dumping the Contents of a Table to a File G-7
Generating a Dynamic Predicate G-9
Summary G-11
H Oracle Database Architectural Components
Objectives H-2
Oracle Database Architecture: Overview H-3
Oracle Database Server Structures H-4
Connecting to the Database H-5
Interacting with an Oracle Database H-6
Oracle Memory Architecture H-8
Process Architecture H-10
Database Writer Process H-12
Log Writer Process H-13
Checkpoint Process H-14
System Monitor Process H-15
Process Monitor Process H-16
Oracle Database Storage Architecture H-17

xiii
Logical and Physical Database Structures H-19
Processing a SQL Statement H-21
Processing a Query H-22
Shared Pool H-23
Database Buffer Cache H-25
Program Global Area (PGA) H-26
Processing a DML Statement H-27
Redo Log Buffer H-29
Rollback Segment H-30
COMMIT Processing H-31
Summary of the Oracle Database Architecture H-33
Summary H-34
I Regular Expression Support
Objectives I-2
What Are Regular Expressions? I-3
Benefits of Using Regular Expressions I-4
Using the Regular Expressions Functions and Conditions in SQL and PL/SQL I-5
What Are Metacharacters? I-6
Using Metacharacters with Regular Expressions I-7
Regular Expressions Functions and Conditions: Syntax I-9
Performing a Basic Search by Using the REGEXP_LIKE Condition I-10
Replacing Patterns by Using the REGEXP_REPLACE Function I-11
Finding Patterns by Using the REGEXP_INSTR Function I-12
Extracting Substrings by Using the REGEXP_SUBSTR Function I-13
Subexpressions I-14
Using Subexpressions with Regular Expression Support I-15
Why Access the nth Subexpression? I-16
REGEXP_SUBSTR: Example I-17
Using the REGEXP_COUNT Function I-18
Regular Expressions and Check Constraints: Examples I-19
Quiz I-20
Summary I-21 OracleUniversityandEgabiSolutionsuseonly

Introduction

Oracle Database 12c: SQL Workshop II 1 - 2
Lesson Objectives
After completing this lesson, you should be able to:
• Discuss the goals of the course
• Describe the database schema and tables that are used in
the course
• Identify the available environments that can be used in the
course
• Review some of the basic concepts of SQL

Lesson Agenda
• Course objectives and course agenda
• The database schema, the appendixes and practices, and
development environments used in this course
• Review of some basic SQL concepts
• Oracle Database 12c documentation and additional
resources

Course Objectives
After completing this course, you should be able to:
• Manage objects with data dictionary views
• Create schema objects
• Manage schema objects
• Write multiple-column subqueries
• Use scalar and correlated subqueries
• Control user access to specific database objects
• Add new users with different levels of access privileges
• Manipulate large data sets in the Oracle database by using
subqueries
• Manage data in different time zones

The Oracle Database: SQL Workshop I course offers you an introduction to Oracle Database
technology. In this course, you learn the basic concepts of relational databases and the
powerful SQL programming language. This course provides the essential SQL skills that
enable you to write queries against single and multiple tables, manipulate data in tables,
create database objects, and query metadata.
Course Prerequisites
The Oracle Database: SQL Workshop I course is a prerequisite
for this course.

Course Agenda
• Day 1:
– Introduction
– Introduction to Data Dictionary Views
– Creating Sequence, Synonyms, and Indexes
– Creating Views
– Managing Schema Objects
• Day 2:
– Retrieving Data by Using Subqueries
– Manipulating Data by Using Subqueries
– Controlling User Access
– Manipulating Data
– Managing Data in Different Time Zones

Lesson Agenda
resources

This course uses data from the following tables:
Table Descriptions
• The EMPLOYEES table contains information about all the employees, such as their first
and last names, job IDs, salaries, hire dates, department IDs, and manager IDs. This
table is a child of the DEPARTMENTS table.
• The DEPARTMENTS table contains information such as the department ID, department
name, manager ID, and location ID. This table is the primary key table to the
EMPLOYEES table.
• The LOCATIONS table contains department location information. It contains location ID,
street address, city, state province, postal code, and country ID information. It is the
primary key table to the DEPARTMENTS table and is a child of the COUNTRIES table.
• The COUNTRIES table contains the country names, country IDs, and region IDs. It is a
child of the REGIONS table. This table is the primary key table to the LOCATIONS table.
• The REGIONS table contains region IDs and region names of the various countries. It is
a primary key table to the COUNTRIES table.
Tables Used in This Course
JOB_HISTORY
employee_id
start_date
end_date
job_id
department_id
DEPARTMENTS
department_id
department_name
manager_id
location_id
LOCATIONS
location_id
street_address
postal_code
city
state_province
country_id
JOBS
job_id
job_title
min_salary
max_salary
EMPLOYEES
employee_id
first_name
last_name
email
phone_number
hire_date
job_id
salary
commission_pct
manager_id
department_id
COUNTRIES
country_id
country_name
region_id
REGIONS
region_id
region_name
JOB_GRADES
grade_level
lowest_sal
highest_sal

• The JOB_GRADES table identifies a salary range per job grade. The salary ranges do
not overlap.
• The JOB_HISTORY table stores job history of the employees.
• The JOBS table contains job titles and salary ranges.

Appendixes and Practices Used in This Course
• Appendix A: Table Descriptions
• Appendix B: Using SQL Developer
• Appendix C: Using SQL* Plus
• Appendix D: Commonly Used SQL Commands
• Appendix E: Generating Reports by Grouping Related
Data
• Appendix F: Hierarchical Retrieval
• Appendix G: Writing Advanced Scripts
• Appendix H: Oracle Database Architectural Components
• Appendix I : Regular Expression Support
• Practices and Solutions
• Additional Practices and Solutions

SQL Developer
This course has been developed using Oracle SQL Developer as the tool for running the SQL
statements discussed in the examples in the slide and the practices.
SQL*Plus
The SQL*Plus environment may also be used to run all SQL commands covered in this
course.
Note
• See Appendix B titled “Using SQL Developer” for information about using SQL
Developer.
• See Appendix C titled “Using SQL*Plus” for information about using SQL*Plus.
Development Environments
There are two development environments for this course:
• The primary tool is Oracle SQL Developer.
• You can also use SQL*Plus command-line interface.
SQL*Plus
SQL Developer

The next few slides provide a brief overview of some of the basic concepts that you learned in
the course titled Oracle Database: SQL Workshop I.
Lesson Agenda
resources

You can restrict the rows that are returned from the query by using the WHERE clause. A
WHERE clause contains a condition that must be met, and it directly follows the FROM clause.
The WHERE clause can compare values in columns, literal values, arithmetic expression, or
functions. It consists of three elements:
• Column name
• Comparison condition
• Column name, constant, or list of values
You use comparison conditions in the WHERE clause in the following format:
... WHERE expr operator value
Apart from those mentioned in the slide, you use other comparison conditions such as =, <, >,
<>, <=, and >=.
Three logical operators are available in SQL:
• AND
• OR
• NOT
Review of Restricting Data
• Restrict the rows that are returned by using the WHERE
clause.
• Use comparison conditions to compare one expression
with another value or expression.
• Use logical conditions to combine the result of two
component conditions and produce a single result based
on those conditions.
Operator Meaning
BETWEEN
...AND...
Between two values (inclusive)
IN(set) Match any of a list of values
LIKE Match a character pattern

The order of rows that are returned in a query result is undefined. The ORDER BY clause can
be used to sort the rows. If you use the ORDER BY clause, it must be the last clause of the
SQL statement. You can specify an expression, an alias, or a column position as the sort
condition.
Syntax
SELECT expr
FROM table
[WHERE condition(s)]
[ORDER BY {column, expr, numeric_position} [ASC|DESC]];
In the syntax:
ORDER BY Specifies the order in which the retrieved rows are displayed
ASC Orders the rows in ascending order (This is the default order.)
DESC Orders the rows in descending order
If the ORDER BY clause is not used, the sort order is undefined, and the Oracle Server may not
fetch rows in the same order for the same query twice. Use the ORDER BY clause to display
the rows in a specific order.
Review of Sorting Data
• Sort retrieved rows with the ORDER BY clause:
– ASC: Ascending order, default
– DESC: Descending order
• The ORDER BY clause comes last in the SELECT
statement:
SELECT last_name, job_id, department_id, hire_date
FROM employees
ORDER BY hire_date ;
…

There are two types of functions:
• Single-row functions
• Multiple-row functions
Single-Row Functions
These functions operate only on single rows and return one result per row. There are different
types of single-row functions such as character, number, date, conversion, and general
functions.
Multiple-Row Functions
Functions can manipulate groups of rows to give one result per group of rows. These
functions are also known as group functions.
Review of SQL Functions
Single-row
functions
Multiple-row
functions
Return one result
per row
Return one result
per set of rows
Functions

The following are different types of single-row functions:
• Character functions: Accept character input and can return both character and number
values
• Number functions: Accept numeric input and return numeric values
• Date functions: Operate on values of the DATE data type (All date functions return a
value of the DATE data type, except the MONTHS_BETWEEN function, which returns a
number.)
• Conversion functions: Convert a value from one data type to another
• General functions:
- NVL
- NVL2
- NULLIF
- COALESCE
- CASE
- DECODE
Review of Single-Row Functions
Conversion Date
Number
Single-row
functions
General
Character

Each of the functions accepts an argument. The following table identifies the options that you
can use in the syntax:
Function Description
AVG([DISTINCT|ALL]n) Average value of n, ignoring null values
COUNT({*|[DISTINCT|ALL]expr}) Number of rows, where expr evaluates to
something other than null (count all selected rows
using *, including duplicates and rows with nulls)
MAX([DISTINCT|ALL]expr) Maximum value of expr, ignoring null values
MIN([DISTINCT|ALL]expr) Minimum value of expr, ignoring null values
STDDEV([DISTINCT|ALL]n) Standard deviation of n, ignoring null values
SUM([DISTINCT|ALL]n) Sum values of n, ignoring null values
VARIANCE([DISTINCT|ALL]n) Variance of n, ignoring null values
Review of Types of Group Functions
• AVG
• COUNT
• MAX
• MIN
• STDDEV
• SUM
• VARIANCE
Group
functions

You can build powerful statements out of simple ones by using subqueries. Subqueries are
useful when a query is based on a search criterion with unknown intermediate values.
You can place the subquery in a number of SQL clauses, including the following:
• WHERE clause
• HAVING clause
• FROM clause
The subquery (inner query) executes once before the main query (outer query). The result of
the subquery is used by the main query.
A single-row subquery uses a single-row operator such as =, >, <, >=, <=, or <>. With a
multiple-row subquery, you use a multiple-row operator such as IN, ANY, or ALL.
Example: Display details of employees whose salary is equal to the minimum salary.
SELECT last_name, salary, job_id
FROM employees
WHERE salary = (SELECT MIN(salary)
FROM employees );
Review of Using Subqueries
• A subquery is a SELECT statement nested in a clause of
another SELECT statement.
• Syntax:
• Types of subqueries:
Single-row subquery Multiple-row subquery
Returns only one row Returns more than one row
Uses single-row comparison
operators
Uses multiple-row comparison
operators
SELECT select_list
FROM table
WHERE expr operator
(SELECT select_list
FROM table );

In the example, the MIN group function returns a single value to the outer query.
Note: In this course, you learn how to use multiple-column subqueries. Multiple-column
subqueries return more than one column from the inner SELECT statement.

When you want to add, update, or delete data in the database, you execute a DML statement.
A collection of DML statements that form a logical unit of work is called a transaction. You can
add new rows to a table by using the INSERT statement. With the following syntax, only one
row is inserted at a time.
INSERT INTO table [(column [, column…])]
VALUES (value[, value...]);
You can use the INSERT statement to add rows to a table where the values are derived from
existing tables. In place of the VALUES clause, you use a subquery. The number of columns
and their data types in the column list of the INSERT clause must match the number of values
and their data types in the subquery.
The UPDATE statement modifies specific rows if you specify the WHERE clause.
UPDATE table
SET column = value [, column = value, ...]
[WHERE condition];
Review of Managing Tables Using DML
Statements
A data manipulation language (DML) statement is executed
when you:
• Add new rows to a table
• Modify existing rows in a table
• Remove existing rows from a table
Function Description
INSERT Adds a new row to the table
UPDATE Modifies existing rows in the table
DELETE Removes existing rows from the table
MERGE Updates, inserts, or deletes a row conditionally
into/from a table

You can remove existing rows by using the DELETE statement. You can delete specific rows
by specifying the WHERE clause in the DELETE statement.
DELETE [FROM] table
[WHERE condition];
You learn about the MERGE statement in the lesson titled “Manipulating Data.”

Lesson Agenda
resources

Navigate to http://www.oracle.com/pls/db102/homepage to access the Oracle Database 10g
documentation library.
Navigate to http://www.oracle.com/pls/db112/homepage to access the Oracle Database 11g
Release 2 documentation library.
Oracle Database SQL Documentation
• Oracle Database New Features Guide
• Oracle Database Reference
• Oracle Database SQL Language Reference
• Oracle Database Concepts
• Oracle Database SQL Developer User’s Guide Release 3.2

Additional Resources
For additional information about the new Oracle 12c SQL, refer
to the following:
• Oracle Database 12c: New Features Self Studies
• Oracle by Example series (OBE): Oracle Database 12c
• Oracle Learning Library:
– http://www.oracle.com/goto/oll

Summary
In this lesson, you should have learned how to:
• Discuss the goals of the course
• Describe the database schema and tables that are used in
the course
• Identify the available environments that can be used in the
course
• Recall some of the basic concepts of SQL

In this practice, you use SQL Developer to execute SQL statements.
Note: All written practices use SQL Developer as the development environment. Although it is
recommended that you use SQL Developer, you can also use the SQL*Plus environment that
is available in this course.
Practice 1: Overview
This practice covers the following topics:
• Running the SQL Developer online tutorial
• Starting SQL Developer and creating a new database
connection and browsing the tables
• Executing SQL statements using the SQL Worksheet
• Running some basic SQL commands

Introduction to Data Dictionary Views

In this lesson, you are introduced to the data dictionary views. You learn that the dictionary
views can be used to retrieve metadata and create reports about your schema objects.
Objectives
• Use the data dictionary views to research data on your
objects
• Query various data dictionary views

Lesson Agenda
• Introduction to data dictionary
• Querying the dictionary views for the following:
– Table information
– Column information
– Constraint information
• Adding a comment to a table and querying the dictionary
views for comment information

User tables are tables created by the user and contain business data, such as EMPLOYEES.
There is another collection of tables and views in the Oracle database known as the data
dictionary. This collection is created and maintained by the Oracle Server and contains
information about the database. The data dictionary is structured in tables and views, just like
other database data. Not only is the data dictionary central to every Oracle database, but it is
also an important tool for all users, from end users to application designers and database
administrators.
You use SQL statements to access the data dictionary. Because the data dictionary is read-
only, you can issue only queries against its tables and views.
You can query the dictionary views that are based on the dictionary tables to find information
such as:
• Definitions of all schema objects in the database (tables, views, indexes, synonyms,
sequences, procedures, functions, packages, triggers, and so on)
• Default values for columns
• Integrity constraint information
• Names of Oracle users
• Privileges and roles that each user has been granted
• Other general database information
Data Dictionary
Oracle Server
Tables containing
business data:
EMPLOYEES
DEPARTMENTS
LOCATIONS
JOB_HISTORY
...
Data dictionary
views:
DICTIONARY
USER_OBJECTS
USER_TABLES
USER_TAB_COLUMNS
...

Underlying base tables store information about the associated database. Only the Oracle
Server should write to and read from these tables. You rarely access them directly.
There are several views that summarize and display the information stored in the base tables
of the data dictionary. These views decode the base table data into useful information (such
as user or table names) using joins and WHERE clauses to simplify the information. Most users
are given access to the views rather than the base tables.
The Oracle user SYS owns all base tables and user-accessible views of the data dictionary.
No Oracle user should ever alter (UPDATE, DELETE, or INSERT) any rows or schema objects
contained in the SYS schema, because such activity can compromise data integrity.
Data Dictionary Structure
Consists of:
– Base tables
– User-accessible views
Oracle Server

The data dictionary consists of sets of views. In many cases, a set consists of three views
containing similar information and distinguished from each other by their prefixes. For
example, there is a view named USER_OBJECTS, another named ALL_OBJECTS, and a third
named DBA_OBJECTS.
These three views contain similar information about objects in the database, except that the
scope is different. USER_OBJECTS contains information about objects that you own or you
created. ALL_OBJECTS contains information about all objects to which you have access.
DBA_OBJECTS contains information about all objects that are owned by all users. For views
that are prefixed with ALL or DBA, there is usually an additional column in the view named
OWNER to identify who owns the object.
There is also a set of views that is prefixed with v$. These views are dynamic in nature and
hold information about performance. Dynamic performance tables are not true tables, and
they should not be accessed by most users. However, database administrators can query and
create views on the tables and grant access to those views to other users. This course does
not go into details about these views.
Data Dictionary Structure
View naming convention:
View Prefix Purpose
USER User’s view (what is in your schema; what you
own)
ALL Expanded user’s view (what you can access)
DBA Database administrator’s view (what is in
everyone’s schemas)
V$ Performance-related data

To familiarize yourself with the dictionary views, you can use the dictionary view named
DICTIONARY. It contains the name and short description of each dictionary view to which you
have access.
You can write queries to search for information about a particular view name, or you can
search the COMMENTS column for a word or phrase. In the example shown, the DICTIONARY
view is described. It has two columns. The SELECT statement retrieves information about the
dictionary view named USER_OBJECTS. The USER_OBJECTS view contains information about
all the objects that you own.
You can write queries to search the COMMENTS column for a word or phrase. For example, the
following query returns the names of all views that you are permitted to access in which the
COMMENTS column contains the word columns:
SELECT table_name
FROM dictionary
WHERE LOWER(comments) LIKE '%columns%';
Note: The names in the data dictionary are in uppercase.
How to Use the Dictionary Views
Start with DICTIONARY. It contains the names and descriptions
of the dictionary tables and views.
DESCRIBE DICTIONARY
SELECT *
FROM dictionary
WHERE table_name = 'USER_OBJECTS';

You can query the USER_OBJECTS view to see the names and types of all the objects in your
schema. There are several columns in this view:
• OBJECT_NAME: Name of the object
• OBJECT_ID: Dictionary object number of the object
• OBJECT_TYPE: Type of object (such as TABLE, VIEW, INDEX, SEQUENCE)
• CREATED: Time stamp for the creation of the object
• LAST_DDL_TIME: Time stamp for the last modification of the object resulting from a
data definition language (DDL) command
• STATUS: Status of the object (VALID, INVALID, or N/A)
• GENERATED: Was the name of this object system-generated? (Y|N)
Note: This is not a complete listing of the columns. For a complete listing, see
“USER_OBJECTS” in the Oracle Database Reference.
You can also query the ALL_OBJECTS view to see a listing of all objects to which you have
access.
USER_OBJECTS and ALL_OBJECTS Views
USER_OBJECTS:
• Query USER_OBJECTS to see all the objects that you own.
• Using USER_OBJECTS, you can obtain a listing of all object
names and types in your schema, plus the following
information:
– Date created
– Date of last modification
– Status (valid or invalid)
ALL_OBJECTS:
• Query ALL_OBJECTS to see all the objects to which you
have access.

The example shows the names, types, dates of creation, and status of all objects that are
owned by this user.
The OBJECT_TYPE column holds the values of either TABLE, VIEW, SEQUENCE, INDEX,
PROCEDURE, FUNCTION, PACKAGE, or TRIGGER.
The STATUS column holds a value of VALID, INVALID, or N/A. Although tables are always
valid, the views, procedures, functions, packages, and triggers may be invalid.
The CAT View
For a simplified query and output, you can query the CAT view. This view contains only two
columns: TABLE_NAME and TABLE_TYPE. It provides the names of all your INDEX, TABLE,
CLUSTER, VIEW, SYNONYM, SEQUENCE, or UNDEFINED objects.
Note: CAT is a synonym for USER_CATALOG—a view that lists tables, views, synonyms and
sequences owned by the user.
USER_OBJECTS View
SELECT object_name, object_type, created, status
FROM user_objects
ORDER BY object_type;
…

Lesson Agenda

You can use the USER_TABLES view to obtain the names of all your tables. The
USER_TABLES view contains information about your tables. In addition to providing the table
name, it contains detailed information about the storage.
The TABS view is a synonym of the USER_TABLES view. You can query it to see a listing of
tables that you own:
SELECT table_name
FROM tabs;
Note: For a complete listing of the columns in the USER_TABLES view, see “USER_TABLES”
in the Oracle Database Reference.
You can also query the ALL_TABLES view to see a listing of all tables to which you have
access.
Table Information
USER_TABLES:
DESCRIBE user_tables
SELECT table_name
FROM user_tables;
…
…

You can query the USER_TAB_COLUMNS view to find detailed information about the columns
in your tables. Although the USER_TABLES view provides information about your table names
and storage, detailed column information is found in the USER_TAB_COLUMNS view.
This view contains information such as:
• Column names
• Column data types
• Length of data types
• Precision and scale for NUMBER columns
• Whether nulls are allowed (Is there a NOT NULL constraint on the column?)
• Default value
Note: For a complete listing and description of the columns in the USER_TAB_COLUMNS view,
see “USER_TAB_COLUMNS” in the Oracle Database Reference.
Column Information
USER_TAB_COLUMNS:
DESCRIBE user_tab_columns
…

By querying the USER_TAB_COLUMNS table, you can find details about your columns such as
the names, data types, data type lengths, null constraints, and default value for a column.
The example shown displays the columns, data types, data lengths, and null constraints for
the EMPLOYEES table. Note that this information is similar to the output from the DESCRIBE
command.
To view information about columns set as unused, you use the USER_UNUSED_COL_TABS
dictionary view.
Note: Names of the objects in Data Dictionary are in uppercase.
Column Information
SELECT column_name, data_type, data_length,
data_precision, data_scale, nullable
FROM user_tab_columns
WHERE table_name = 'EMPLOYEES';

You can find out the names of your constraints, the type of constraint, the table name to which
the constraint applies, the condition for check constraints, foreign key constraint information,
deletion rule for foreign key constraints, the status, and many other types of information about
your constraints.
Note: For a complete listing and description of the columns in the USER_CONSTRAINTS view,
see “USER_CONSTRAINTS” in the Oracle Database Reference.
Constraint Information
• USER_CONSTRAINTS describes the constraint definitions
on your tables.
• USER_CONS_COLUMNS describes columns that are owned
by you and that are specified in constraints.
DESCRIBE user_constraints
…

In the example shown, the USER_CONSTRAINTS view is queried to find the names, types,
check conditions, name of the unique constraint that the foreign key references, deletion rule
for a foreign key, and status for constraints on the EMPLOYEES table.
The CONSTRAINT_TYPE can be:
• C (check constraint on a table, or NOT NULL)
• P (primary key)
• U (unique key)
• R (referential integrity)
• V (with check option, on a view)
• O (with read-only, on a view)
The DELETE_RULE can be:
• CASCADE: If the parent record is deleted, the child records are deleted, too.
• SET NULL: If the parent record is deleted, change the respective child record to null.
• NO ACTION: A parent record can be deleted only if no child records exist.
The STATUS can be:
• ENABLED: Constraint is active.
• DISABLED: Constraint is made not active.
USER_CONSTRAINTS: Example
SELECT constraint_name, constraint_type,
search_condition, r_constraint_name,
delete_rule, status
FROM user_constraints

To find the names of the columns to which a constraint applies, query the
USER_CONS_COLUMNS dictionary view. This view tells you the name of the owner of a
constraint, the name of the constraint, the table that the constraint is on, the names of the
columns with the constraint, and the original position of column or attribute in the definition of
the object.
Note: A constraint may apply to more than one column.
You can also write a join between USER_CONSTRAINTS and USER_CONS_COLUMNS to create
customized output from both tables.
Querying USER_CONS_COLUMNS
DESCRIBE user_cons_columns
SELECT constraint_name, column_name
FROM user_cons_columns
…

Lesson Agenda

You can add a comment of up to 4,000 bytes about a column, table, view, or snapshot by
using the COMMENT statement. The comment is stored in the data dictionary and can be
viewed in one of the following data dictionary views in the COMMENTS column:
• ALL_COL_COMMENTS
• USER_COL_COMMENTS
• ALL_TAB_COMMENTS
• USER_TAB_COMMENTS
Syntax
COMMENT ON {TABLE table | COLUMN table.column}
IS 'text';
In the syntax:
table Is the name of the table
column Is the name of the column in a table
text Is the text of the comment
You can drop a comment from the database by setting it to empty string (''):
COMMENT ON TABLE employees IS '';
Adding Comments to a Table
• You can add comments to a table or column by using the
COMMENT statement:
• Comments can be viewed through the data dictionary
views:
– ALL_COL_COMMENTS
– USER_COL_COMMENTS
– ALL_TAB_COMMENTS
– USER_TAB_COMMENTS
COMMENT ON TABLE employees
IS 'Employee Information';
COMMENT ON COLUMN employees.first_name
IS 'First name of the employee';

Answer: e
Quiz
The dictionary views that are based on the dictionary tables
contain information such as:
a. Definitions of all the schema objects in the database
b. Default values for the columns
c. Integrity constraint information
d. Privileges and roles that each user has been granted
e. All of the above

In this lesson, you learned about some of the dictionary views that are available to you. You
can use these dictionary views to find information about your tables, constraints, views,
sequences, and synonyms.
Summary
In this lesson, you should have learned how to find information
about your objects through the following dictionary views:
• DICTIONARY
• USER_OBJECTS
• USER_TABLES
• USER_TAB_COLUMNS
• USER_CONSTRAINTS
• USER_CONS_COLUMNS

In this practice, you query the dictionary views to find information about objects in your
schema.
• Querying the dictionary views for table and column
information
• Querying the dictionary views for constraint information

Creating Sequences, Synonyms, and Indexes

In this lesson, you are introduced to the sequence, synonyms, and index objects. You learn
the basics of creating and using sequences, synonyms and indexes.
Objectives
• Create, maintain, and use sequences
• Create private and public synonyms
• Create and maintain indexes
• Query various data dictionary views to find information for
sequences, synonyms, and indexes

Lesson Agenda
• Overview of sequences:
– Creating, using, and modifying a sequence
– Cache sequence values
– NEXTVAL and CURRVAL pseudocolumns
– SQL column defaulting using a sequence
• Overview of synonyms
– Creating, dropping synonyms
• Overview of indexes
– Creating indexes
– Using the CREATE TABLE statement
– Creating function-based indexes
– Creating multiple indexes on the same set of columns
– Removing indexes

There are several other objects in a database in addition to tables.
With views, you can present and hide data from the tables.
Many applications require the use of unique numbers as primary key values. You can either
build code into the application to handle this requirement or use a sequence to generate
unique numbers.
If you want to improve the performance of data retrieval queries, you should consider creating
an index. You can also use indexes to enforce uniqueness on a column or a collection of
columns.
You can provide alternative names for objects by using synonyms.
Database Objects
Logically represents subsets of data from one or
more tables
View
Generates numeric valuesSequence
Basic unit of storage; composed of rowsTable
Gives alternative names to objectsSynonym
Improves the performance of data retrieval
queries
Index
DescriptionObject

A schema is a collection of logical structures of data or schema objects. A schema is owned
by a database user and has the same name as that user. Each user owns a single schema.
Schema objects can be created and manipulated with SQL and include tables, views,
synonyms, sequences, stored procedures, indexes, clusters, and database links.
If a table does not belong to the user, the owner’s name must be prefixed to the table. For
example, if there are schemas named USERA and USERB, and both have an EMPLOYEES
table, then if USERA wants to access the EMPLOYEES table that belongs to USERB, USERA
must prefix the table name with the schema name:
SELECT *
FROM userb.employees;
If USERB wants to access the EMPLOYEES table that is owned by USERA, USERB must prefix
the table name with the schema name:
SELECT *
FROM usera.employees;
Referencing Another User’s Tables
• Tables belonging to other users are not in the user’s
schema.
• You should use the owner’s name as a prefix to those
tables.
USERBUSERA
SELECT *
FROM userB.employees;
SELECT *
FROM userA.employees;

A sequence is a user-created database object that can be shared by multiple users to
generate integers.
You can define a sequence to generate unique values or to recycle and use the same
numbers again.
A typical usage for sequences is to create a primary key value, which must be unique for each
row. A sequence is generated and incremented (or decremented) by an internal Oracle
routine. This can be a time-saving object, because it can reduce the amount of application
code needed to write a sequence-generating routine.
Sequence numbers are stored and generated independent of tables. Therefore, the same
sequence can be used for multiple tables.
Sequences
A sequence:
• Can automatically generate unique numbers
• Is a shareable object
• Can be used to create a primary key value
• Replaces application code
• Speeds up the efficiency of accessing sequence values
when cached in memory
2 4
3 5
6 8
7
10
91

Automatically generate sequential numbers by using the CREATE SEQUENCE statement.
In the syntax:
sequence Is the name of the sequence generator
INCREMENT BY n Specifies the interval between sequence numbers, where
n is an integer (If this clause is omitted, the sequence
increments by 1.)
START WITH n Specifies the first sequence number to be generated (If
this clause is omitted, the sequence starts with 1.)
MAXVALUE n Specifies the maximum value the sequence can generate
NOMAXVALUE Specifies a maximum value of 10^27 for an ascending
sequence and –1 for a descending sequence (This is the
default option.)
MINVALUE n Specifies the minimum sequence value
NOMINVALUE Specifies a minimum value of 1 for an ascending
sequence and –(10^26) for a descending sequence (This
is the default option.)
CREATE SEQUENCE Statement: Syntax
Define a sequence to generate sequential numbers
automatically:
CREATE SEQUENCE [ schema. ] sequence
[ { INCREMENT BY | START WITH } integer
| { MAXVALUE integer | NOMAXVALUE }
| { MINVALUE integer | NOMINVALUE }
| { CYCLE | NOCYCLE }
| { CACHE integer | NOCACHE }
| { ORDER | NOORDER }
];

ORDER Specify ORDER to guarantee that sequence numbers are
generated in order of request. This clause is useful if you
are using the sequence numbers as timestamps.
NOORDER Specify NOORDER if you do not want to guarantee that
sequence numbers are generated in order of request.
This is the default.
CYCLE | NOCYCLE Specifies whether the sequence continues to generate
values after reaching its maximum or minimum value
(NOCYCLE is the default option.)
CACHE n | NOCACHE Specifies how many values the Oracle Server pre-
allocates and keeps in memory (By default, the Oracle
server caches 20 values.)

The example in the slide creates a sequence named DEPT_DEPTID_SEQ to be used for the
DEPARTMENT_ID column of the DEPARTMENTS table. The sequence starts at 280, does not
allow caching, and does not cycle.
Do not use the CYCLE option if the sequence is used to generate primary key values, unless
you have a reliable mechanism that purges old rows faster than the sequence cycles.
For more information, see the “CREATE SEQUENCE” section in the Oracle Database SQL
Language Reference for Oracle Database 12c.
Note: The sequence is not tied to a table. Generally, you should name the sequence after its
intended use. However, the sequence can be used anywhere, regardless of its name.
Creating a Sequence
• Create a sequence named DEPT_DEPTID_SEQ to be used
for the primary key of the DEPARTMENTS table.
• Do not use the CYCLE option.
CREATE SEQUENCE dept_deptid_seq
INCREMENT BY 10
START WITH 280
MAXVALUE 9999
NOCACHE
NOCYCLE;

After you create your sequence, it generates sequential numbers for use in your tables.
Reference the sequence values by using the NEXTVAL and CURRVAL pseudocolumns.
The NEXTVAL pseudocolumn is used to extract successive sequence numbers from a
specified sequence. You must qualify NEXTVAL with the sequence name. When you
reference sequence.NEXTVAL, a new sequence number is generated and the current
sequence number is placed in CURRVAL.
The CURRVAL pseudocolumn is used to refer to a sequence number that the current user has
just generated. However, NEXTVAL must be used to generate a sequence number in the
current user’s session before CURRVAL can be referenced. You must qualify CURRVAL with
the sequence name. When you reference sequence.CURRVAL, the last value returned to
that user’s process is displayed.
NEXTVAL and CURRVAL Pseudocolumns
• NEXTVAL returns the next available sequence value. It
returns a unique value every time it is referenced, even for
different users.
• CURRVAL obtains the current sequence value.
• NEXTVAL must be issued for that sequence before
CURRVAL contains a value.

Rules for Using NEXTVAL and CURRVAL
You can use NEXTVAL and CURRVAL in the following contexts:
• The SELECT list of a SELECT statement that is not part of a subquery
• The SELECT list of a subquery in an INSERT statement
• The VALUES clause of an INSERT statement
• The SET clause of an UPDATE statement
You cannot use NEXTVAL and CURRVAL in the following contexts:
• The SELECT list of a view
• A SELECT statement with the DISTINCT keyword
• A SELECT statement with GROUP BY, HAVING, or ORDER BY clauses
• A subquery in a SELECT, DELETE, or UPDATE statement
For more information, see the “Pseudocolumns” and “CREATE SEQUENCE” sections in Oracle
Database SQL Language Reference for Oracle Database 12c.

The example in the slide inserts a new department in the DEPARTMENTS table. It uses the
DEPT_DEPTID_SEQ sequence to generate a new department number as follows.
You can view the current value of the sequence using the sequence_name.CURRVAL, as
shown in the second example in the slide. The output of the query is shown below:
Suppose that you now want to hire employees to staff the new department. The INSERT
statement to be executed for all new employees can include the following code:
INSERT INTO employees (employee_id, department_id, ...)
VALUES (employees_seq.NEXTVAL, dept_deptid_seq .CURRVAL, ...);
Note: The preceding example assumes that a sequence called EMPLOYEE_SEQ has already
been created to generate new employee numbers.
Using a Sequence
• Insert a new department named “Support” in location ID
2500:
• View the current value for the DEPT_DEPTID_SEQ
sequence:
INSERT INTO departments(department_id,
department_name, location_id)
VALUES (dept_deptid_seq.NEXTVAL,
'Support', 2500);
SELECT dept_deptid_seq.CURRVAL
FROM dual;

SQL syntax for column defaults has been enhanced so that it allows
<sequence>.nextval, <sequence>.currval as a SQL column defaulting expression
for numeric columns, where <sequence> is an Oracle database sequence.
The DEFAULT expression can include the sequence pseudocolumns CURRVAL and NEXTVAL,
as long as the sequence exists and you have the privileges necessary to access it. The user
inserting into a table must have access privileges to the sequence. If the sequence is
dropped, subsequent insert DMLs where expr is used for defaulting will result in a compilation
error.
In the slide example, sequence s1 is created, which starts from 1.
SQL Column defaulting using a Sequence
• SQL syntax for column defaults allow
<sequence>.nextval, <sequence>.currval as a
SQL column defaulting expression for numeric columns,
where <sequence> is an Oracle database sequence.
• The DEFAULT expression can include the sequence
pseudocolumns CURRVAL and NEXTVAL, as long as the
sequence exists and you have the privileges necessary to
access it.
CREATE SEQUENCE s1 START WITH 1;
CREATE TABLE emp (a1 NUMBER DEFAULT s1.NEXTVAL NOT
NULL, a2 VARCHAR2(10));
INSERT INTO emp (a2) VALUES (‘john');
INSERT INTO emp (a2) VALUES (‘mark');
SELECT * FROM emp;

You can cache sequences in memory to provide faster access to those sequence values. The
cache is populated the first time you refer to the sequence. Each request for the next
sequence value is retrieved from the cached sequence. After the last sequence value is used,
the next request for the sequence pulls another cache of sequences into memory.
Gaps in the Sequence
Although sequence generators issue sequential numbers without gaps, this action occurs
independently of a commit or rollback. Therefore, if you roll back a statement containing a
sequence, the number is lost.
Another event that can cause gaps in the sequence is a system crash. If the sequence
caches values in memory, those values are lost if the system crashes.
Because sequences are not tied directly to tables, the same sequence can be used for
multiple tables. However, if you do so, each table can contain gaps in the sequential numbers.
Caching Sequence Values
• Caching sequence values in memory gives faster access
to those values.
• Gaps in sequence values can occur when:
– A rollback occurs
– The system crashes
– A sequence is used in another table

If you reach the MAXVALUE limit for your sequence, no additional values from the sequence
are allocated and you will receive an error indicating that the sequence exceeds the
MAXVALUE. To continue to use the sequence, you can modify it by using the ALTER
SEQUENCE statement.
Syntax
ALTER SEQUENCE sequence
[INCREMENT BY n]
[{MAXVALUE n | NOMAXVALUE}]
[{MINVALUE n | NOMINVALUE}]
[{CYCLE | NOCYCLE}]
[{CACHE n | NOCACHE}];
In the syntax, sequence is the name of the sequence generator.
For more information, see the section on “ALTER SEQUENCE” in Oracle Database SQL
Modifying a Sequence
Change the increment value, maximum value, minimum value,
cycle option, or cache option:
ALTER SEQUENCE dept_deptid_seq
INCREMENT BY 20
MAXVALUE 999999
NOCACHE
NOCYCLE;

• You must be the owner or have the ALTER privilege for the sequence to modify it. You
must be the owner or have the DROP ANY SEQUENCE privilege to remove it.
• Only future sequence numbers are affected by the ALTER SEQUENCE statement.
• The START WITH option cannot be changed using ALTER SEQUENCE. The sequence
must be dropped and re-created to restart the sequence at a different number.
• Some validation is performed. For example, a new MAXVALUE that is less than the
current sequence number cannot be imposed.
ALTER SEQUENCE dept_deptid_seq
INCREMENT BY 20
MAXVALUE 90
NOCACHE
NOCYCLE;
• The error:
SQL Error: ORA-04009: MAXVALUE cannot be made to be less than the current value
04009. 00000 - "MAXVALUE cannot be made to be less than the current value"
*Cause: the current value exceeds the given MAXVALUE
*Action: make sure that the new MAXVALUE is larger than the current value
Guidelines for Modifying a Sequence
• You must be the owner or have the ALTER privilege for the
sequence.
• Only future sequence numbers are affected.
• The sequence must be dropped and re-created to restart
the sequence at a different number.
• Some validation is performed.
• To remove a sequence, use the DROP statement:
DROP SEQUENCE dept_deptid_seq;

The USER_SEQUENCES view describes all sequences that you own. When you create the
sequence, you specify criteria that are stored in the USER_SEQUENCES view. The columns in
this view are:
• SEQUENCE_NAME: Name of the sequence
• MIN_VALUE: Minimum value of the sequence
• MAX_VALUE: Maximum value of the sequence
• INCREMENT_BY: Value by which the sequence is incremented
• CYCLE_FLAG: Whether sequence wraps around on reaching the limit
• ORDER_FLAG: Whether sequence numbers are generated in order
• CACHE_SIZE: Number of sequence numbers to cache
• LAST_NUMBER: Last sequence number written to disk. If a sequence uses caching, the
number written to disk is the last number placed in the sequence cache. This number is
likely to be greater than the last sequence number that was used. The LAST_NUMBER
column displays the next available sequence number if NOCACHE is specified.
After creating your sequence, it is documented in the data dictionary. Because a sequence is
a database object, you can identify it in the USER_OBJECTS data dictionary table.
You can also confirm the settings of the sequence by selecting from the USER_SEQUENCES
data dictionary view.
Sequence Information
• The USER_SEQUENCES view describes all sequences that
you own.
• Verify your sequence values in the USER_SEQUENCES
data dictionary table.
DESCRIBE user_sequences
SELECT sequence_name, min_value, max_value,
increment_by, last_number
FROM user_sequences;

Lesson Agenda

Synonyms are database object that enable you to call a table by another name.
You can create synonyms to give an alternative name to a table or to an other database
object. For example, you can create a synonym for a table or view, sequence, PL/SQL
program unit, user-defined object type, or another synonym.
Because a synonym is simply an alias, it requires no storage other than its definition in the
data dictionary.
Synonyms can simplify SQL statements for database users. Synonyms are also useful for
hiding the identity and location of an underlying schema object.
Synonyms
A synonym
• Is a database object
• Can be created to give an alternative name to a table or to
an other database object
• Requires no storage other than its definition in the data
dictionary
• Is useful for hiding the identity and location of an
underlying schema object

To refer to a table that is owned by another user, you need to prefix the table name with the
name of the user who created it, followed by a period. Creating a synonym eliminates the
need to qualify the object name with the schema and provides you with an alternative name
for a table, view, sequence, procedure, or other objects. This method can be especially useful
with lengthy object names, such as views.
In the syntax:
PUBLIC Creates a synonym that is accessible to all users
synonym Is the name of the synonym to be created
object Identifies the object for which the synonym is created
Guidelines
• The object cannot be contained in a package.
• A private synonym name must be distinct from all other objects that are owned by the
same user.
• To create a PUBLIC synonym, you must have the CREATE PUBLIC SYNONYM system
privilege.
For more information, see the section on “CREATE SYNONYM” in Oracle Database SQL
Creating a Synonym for an Object
Simplify access to objects by creating a synonym (another
name for an object). With synonyms, you can:
• Create an easier reference to a table that is owned by
another user
• Shorten lengthy object names
CREATE [PUBLIC] SYNONYM synonym
FOR object;

Creating a Synonym
The slide example creates a synonym for the DEPT_SUM_VU view for quicker reference.
The database administrator can create a public synonym that is accessible to all users. The
following example creates a public synonym named DEPT for Alice’s DEPARTMENTS table:
CREATE PUBLIC SYNONYM dept
FOR alice.departments;
Removing a Synonym
To remove a synonym, use the DROP SYNONYM statement. Only the database administrator
can drop a public synonym.
DROP PUBLIC SYNONYM dept;
For more information, see the section on “DROP SYNONYM” in Oracle Database SQL
Creating and Removing Synonyms
• Create a shortened name for the DEPT_SUM_VU view:
• Drop a synonym:
CREATE SYNONYM d_sum
FOR dept_sum_vu;
DROP SYNONYM d_sum;

The USER_SYNONYMS dictionary view describes private synonyms (synonyms that you own).
You can query this view to find your synonyms. You can query ALL_SYNONYMS to find out the
name of all the synonyms that are available to you and the objects on which these synonyms
apply.
The columns in this view are:
• SYNONYM_NAME: Name of the synonym
• TABLE_OWNER: Owner of the object that is referenced by the synonym
• TABLE_NAME: Name of the table or view that is referenced by the synonym
• DB_LINK: Name of the database link reference (if any)
Synonym Information
DESCRIBE user_synonyms
SELECT *
FROM user_synonyms;

Lesson Agenda

An Oracle Server index is a schema object that can speed up the retrieval of rows by using a
pointer and improves the performance of some queries. Indexes can be created explicitly or
automatically. If you do not have an index on the column, a full table scan occurs.
An index provides direct and fast access to rows in a table. Its purpose is to reduce the disk
I/O by using an indexed path to locate data quickly. An index is used and maintained
automatically by the Oracle Server. After an index is created, no direct activity is required by
the user.
Indexes are logically and physically independent of the data in the objects with which they are
associated. This means that they can be created or dropped at any time, and have no effect
on the base tables or other indexes.
Note: When you drop a table, the corresponding indexes are also dropped.
For more information, see the section on “Schema Objects: Indexes” in Oracle Database
Concepts for Oracle Database 12c.
Indexes
An index:
• Is a schema object
• Can be used by the Oracle Server to speed up the retrieval
of rows by using a pointer
• Can reduce disk input/output (I/O) by using a rapid path
access method to locate data quickly
• Is dependent on the table that it indexes
• Is used and maintained automatically by the Oracle Server

You can create two types of indexes.
• Unique index: The Oracle Server automatically creates this index when you define a
column in a table to have a PRIMARY KEY or a UNIQUE constraint. The name of the
index is the name that is given to the constraint.
• Nonunique index: This is an index that a user can create. For example, you can create
the FOREIGN KEY column index for a join in a query to improve the speed of retrieval.
Note: You can manually create a unique index, but it is recommended that you create a
unique constraint, which implicitly creates a unique index.
How Are Indexes Created?
• Automatically: A unique index is created automatically
when you define a PRIMARY KEY or UNIQUE constraint in
a table definition.
• Manually: You can create unique or nonunique index on
columns to speed up access to the rows.

Create an index on one or more columns by issuing the CREATE INDEX statement.
In the syntax:
• index Is the name of the index
• table Is the name of the table
• Column Is the name of the column in the table to be indexed
Specify UNIQUE to indicate that the value of the column (or columns) upon which the index is
based must be unique. Specify BITMAP to indicate that the index is to be created with a
bitmap for each distinct key, rather than indexing each row separately. Bitmap indexes store
the rowids associated with a key value as a bitmap.
For more information, see the section on “CREATE INDEX” in Oracle Database SQL
Creating an Index
• Create an index on one or more columns:
• Improve the speed of query access to the LAST_NAME
column in the EMPLOYEES table:
CREATE INDEX emp_last_name_idx
ON employees(last_name);
CREATE [UNIQUE][BITMAP]INDEX index
ON table (column[, column]...);

In the example in the slide, the CREATE INDEX clause is used with the CREATE TABLE
statement to create a PRIMARY KEY index explicitly. You can name your indexes at the time
of PRIMARY KEY creation to be different from the name of the PRIMARY KEY constraint.
You can query the USER_INDEXES data dictionary view for information about your indexes.
The following example illustrates the database behavior if the index is not explicitly named:
CREATE TABLE EMP_UNNAMED_INDEX
(employee_id NUMBER(6) PRIMARY KEY ,
first_name VARCHAR2(20),
last_name VARCHAR2(25));
SELECT INDEX_NAME, TABLE_NAME
FROM USER_INDEXES
WHERE TABLE_NAME = 'EMP_UNNAMED_INDEX';
CREATE INDEX with the CREATE TABLE Statement
CREATE TABLE NEW_EMP
(employee_id NUMBER(6)
PRIMARY KEY USING INDEX
(CREATE INDEX emp_id_idx ON
NEW_EMP(employee_id)),
last_name VARCHAR2(25));
SELECT INDEX_NAME, TABLE_NAME
FROM USER_INDEXES
WHERE TABLE_NAME = 'NEW_EMP';

Observe that the Oracle Server gives a generic name to the index that is created for the
PRIMARY KEY column.
You can also use an existing index for your PRIMARY KEY column—for example, when you
are expecting a large data load and want to speed up the operation. You may want to disable
the constraints while performing the load and then enable them, in which case having a
unique index on the PRIMARY KEY will still cause the data to be verified during the load.
Therefore, you can first create a nonunique index on the column designated as PRIMARY
KEY, and then create the PRIMARY KEY column and specify that it should use the existing
index. The following examples illustrate this process:
Step 1: Create the table:
CREATE TABLE NEW_EMP2
(employee_id NUMBER(6),
last_name VARCHAR2(25)
);
Step 2: Create the index:
CREATE INDEX emp_id_idx2 ON
new_emp2(employee_id);
Step 3: Create the PRIMARY KEY:
ALTER TABLE new_emp2 ADD PRIMARY KEY (employee_id) USING INDEX
emp_id_idx2;

Function-based indexes defined with the UPPER(column_name)or LOWER(column_name)
keywords allow non-case-sensitive searches. For example, consider the following index:
CREATE INDEX upper_last_name_idx ON emp2 (UPPER(last_name));
This facilitates processing queries such as:
SELECT * FROM emp2 WHERE UPPER(last_name) = 'KING';
The Oracle Server uses the index only when that particular function is used in a query. For
example, the following statement may use the index, but without the WHERE clause, the
Oracle Server may perform a full table scan:
SELECT *
FROM employees
WHERE UPPER (last_name) IS NOT NULL
ORDER BY UPPER (last_name);
Note: For creating a function-based index, you need the QUERY REWRITE system privilege.
The QUERY_REWRITE_ENABLED initialization parameter must be set to TRUE for a function-
based index to be used.
The Oracle Server treats indexes with columns marked DESC as function-based indexes. The
columns marked DESC are sorted in descending order.
CREATE INDEX upper_dept_name_idx
ON dept2(UPPER(department_name));
Function-Based Indexes
• A function-based index is based on expressions.
• The index expression is built from table columns,
constants, SQL functions, and user-defined functions.
SELECT *
FROM dept2
WHERE UPPER(department_name) = 'SALES';

You can create multiple indexes on the same set of columns if the indexes are of different
types, use different partitioning, or have different uniqueness properties. For example, you
can create a B-tree index and a bitmap index on the same set of columns.
Similarly, you can create both a unique and non-unique index on the same set of columns
When you have multiple indexes on the same set of columns, only one of these indexes can
be visible at a time.
Note: Invisible Index – An invisible index is maintained by DML operations. To create an
invisible index, you can use the CREATE INDEX statement with the INVISIBLE keyword.
Creating Multiple Indexes on the Same Set of
Columns
• You can create multiple indexes on the same set of
columns.
• Multiple indexes can be created on the same set of
columns if:
– The indexes are of different types
– The indexes uses different partitioning
– The indexes have different uniqueness properties

The code example shows the creation of a B-tree index, emp_id_name_ix1, on the
employee_id and first_name column of the employees table in the HR schema. After the
creation of the index, it is altered to make it invisible. Then a bitmap index is created on the
employee_id and first_name column of the employees table in the HR schema. The
bitmap index, emp_id_name_ix2, is visible by default.
Example of Creating Multiple Indexes on the
Same Set Of Columns
CREATE INDEX emp_id_name_ix1
ON employees(employee_id, first_name);
ALTER INDEX emp_id_name_ix1 INVISIBLE;
CREATE BITMAP INDEX emp_id_name_ix2
ON employees(employee_id, first_name);

More Is Not Always Better
Having more indexes on a table does not produce faster queries. Each DML operation that is
committed on a table with indexes means that the indexes must be updated. The more
indexes that you have associated with a table, the more effort the Oracle Server must make to
update all the indexes after a DML operation.
When to Create an Index
Therefore, you should create indexes only if:
• The column contains a wide range of values
• The column contains a large number of null values
• One or more columns are frequently used together in a WHERE clause or join condition
• The table is large and most queries are expected to retrieve less than 2% to 4% of the
rows
Remember that if you want to enforce uniqueness, you should define a unique constraint in
the table definition. A unique index is then created automatically.
Index Creation Guidelines
Do not create an index when:
The columns are not often used as a condition in the query
The table is small or most queries are expected to retrieve more than 2%
to 4% of the rows in the table
The table is updated frequently
A column contains a large number of null values
One or more columns are frequently used together in a WHERE clause or
a join condition
A column contains a wide range of values
The indexed columns are referenced as part of an expression
The table is large and most queries are expected to retrieve less than 2%
to 4% of the rows in the table
Create an index when:

You query the USER_INDEXES view to find out the names of your indexes, the table name on
which the index is created, and whether the index is unique.
Note: For a complete listing and description of the columns in the USER_INDEXES view, see
“USER_INDEXES” in the Oracle Database Reference for Oracle Database 12c.
Index Information
• USER_INDEXES provides information about your indexes.
• USER_IND_COLUMNS describes columns of indexes
owned by you and columns of indexes on your tables.
DESCRIBE user_indexes
…

In slide example a, the USER_INDEXES view is queried to find the name of the index, name of
the table on which the index is created, and whether the index is unique.
In slide example b, observe that the Oracle Server gives a generic name to the index that is
created for the PRIMARY KEY column. The EMP_LIB table is created by using the following
code:
CREATE TABLE emp_lib
(book_id NUMBER(6) PRIMARY KEY,
title VARCHAR2(25),
category VARCHAR2(20));
USER_INDEXES: Examples
SELECT index_name, table_name, uniqueness
FROM user_indexes
SELECT index_name, table_name
FROM user_indexes
WHERE table_name = 'EMP_LIB';
a
b
…

The USER_IND_COLUMNS dictionary view provides information such as the name of the
index, name of the indexed table, name of a column within the index, and the column’s
position within the index.
For the slide example, the emp_test table and LNAME_IDX index are created by using the
following code:
CREATE TABLE emp_test AS SELECT * FROM employees;
CREATE INDEX lname_idx ON emp_test(last_name);
Querying USER_IND_COLUMNS
DESCRIBE user_ind_columns
SELECT index_name, column_name,table_name
FROM user_ind_columns
WHERE index_name = 'LNAME_IDX';

You cannot modify indexes. To change an index, you must drop it and then re-create it.
Remove an index definition from the data dictionary by issuing the DROP INDEX statement. To
drop an index, you must be the owner of the index or have the DROP ANY INDEX privilege.
In the syntax, index is the name of the index.
You can drop an index using the ONLINE keyword.
DROP INDEX emp_indx ONLINE;
ONLINE: Specify ONLINE to indicate that DML operations on the table are allowed while
dropping the index.
Note: If you drop a table, indexes and constraints are automatically dropped but views
remain.
Removing an Index
• Remove an index from the data dictionary by using the
DROP INDEX command:
• Remove the emp_last_name_idx index from the data
dictionary:
• To drop an index, you must be the owner of the index or
have the DROP ANY INDEX privilege.
DROP INDEX emp_last_name_idx;
DROP INDEX index;

Answer: b
Note: Indexes are designed to speed up query performance. However, not all indexes are
created manually. The Oracle server automatically creates an index when you define a
column in a table to have a PRIMARY KEY or a UNIQUE constraint.
Quiz
Indexes must be created manually and serve to speed up
access to rows in a table.
a. True
b. False

In this lesson, you should have learned about database objects such as sequences, indexes,
and synonyms.
Summary
• Automatically generate sequence numbers by using a
sequence generator
• Use synonyms to provide alternative names for objects
• Create indexes to improve the speed of query retrieval
• Find information about your objects through the following
dictionary views:
– USER_VIEWS
– USER_SEQUENCES
– USER_SYNONYMS

This lesson’s practice provides you with a variety of exercises in creating and using a
sequence, an index, and a synonym. You also learn how to query the data dictionary views
for sequence, synonyms and index information.
• Creating sequences
• Using sequences
• Querying the dictionary views for sequence information
• Creating synonyms
• Querying the dictionary views for synonyms information
• Creating indexes
• Querying the dictionary views for indexes information

Creating Views

In this lesson, you are introduced to views, and you learn the basics of creating and using
views.
Objectives
After completing this lesson, you should be able to do::
• Create simple and complex views
• Retrieve data from views
• Querying the dictionary views for the view information

Lesson Agenda
• Overview of views
• Creating, modifying, and retrieving data from a view
• Querying the dictionary views for view information
• Data manipulation language (DML) operations on a view
• Dropping a view

There are several other objects in a database in addition to tables.
With views, you can present and hide data from the tables.
Many applications require the use of unique numbers as primary key values. You can either
build code into the application to handle this requirement or use a sequence to generate
unique numbers.
If you want to improve the performance of data retrieval queries, you should consider creating
an index. You can also use indexes to enforce uniqueness on a column or a collection of
columns.
You can provide alternative names for objects by using synonyms.
Database Objects
Logically represents subsets of data from one or
more tables
View
Generates numeric valuesSequence
Basic unit of storage; composed of rowsTable
Gives alternative names to objectsSynonym
Improves the performance of data retrieval
queries
Index
DescriptionObject

You can present logical subsets or combinations of data by creating views of tables. A view is
a schema object , a stored SELECT statement based on a table or another view. A view
contains no data of its own, but is like a window through which data from tables can be
viewed or changed. The tables on which a view is based are called base tables. The view is
stored as a SELECT statement in the data dictionary.
What Is a View?
EMPLOYEES table

• Views restrict access to the data because they display selected columns from the table.
• Views can be used to make simple queries to retrieve the results of complicated queries.
For example, views can be used to query information from multiple tables without the
user knowing how to write a join statement.
• Views provide data independence for ad hoc users and application programs. One view
can be used to retrieve data from several tables.
• Views provide groups of users access to data according to their particular criteria.
For more information, see the “CREATE VIEW” section in Oracle Database SQL Language
Reference for Oracle Database 12c.
Advantages of Views
To restrict
data access
To make complex
queries easy
To provide data
independence
To present different
views of the same
data

There are two classifications for views: simple and complex. The basic difference is related to
the DML (INSERT, UPDATE, and DELETE) operations.
• A simple view is one that:
- Derives data from only one table
- Contains no functions or groups of data
- Can perform DML operations through the view
• A complex view is one that:
- Derives data from many tables
- Contains functions or groups of data
- Does not always allow DML operations through the view
Simple Views and Complex Views
Yes
No
No
One
Simple Views
YesContain functions
YesContain groups of data
One or moreNumber of tables
Not alwaysDML operations through a
view
Complex ViewsFeature

You can create a view by embedding a subquery in the CREATE VIEW statement.
In the syntax:
OR REPLACE Re-creates the view if it already exists. You can use this clause to
change the definition of an existing view without dropping,
re-creating, and regranting object privileges previously granted
on it.
FORCE Creates the view regardless of whether or not the base tables exist
NOFORCE Creates the view only if the base tables exist (This is the default.)
view Is the name of the view
alias Specifies names for the expressions selected by the view’s query
(The number of aliases must match the number of expressions
selected by the view.)
subquery Is a complete SELECT statement (You can use aliases for the
columns in the SELECT list.)
WITH CHECK OPTION Specifies that only those rows that are accessible to the view can
be inserted or updated
Constraint Is the name assigned to the CHECK OPTION constraint
WITH READ ONLY Ensures that no DML operations can be performed on this view
Note: In SQL Developer, click the Run Script icon or press F5 to run the data definition
language (DDL) statements. The feedback messages will be shown on the Script Output
tabbed page.
Creating a View
• You embed a subquery in the CREATE VIEW statement:
• The subquery can contain complex SELECT syntax.
CREATE [OR REPLACE] [FORCE|NOFORCE] VIEW view
[(alias[, alias]...)]
AS subquery
[WITH CHECK OPTION [CONSTRAINT constraint]]
[WITH READ ONLY [CONSTRAINT constraint]];

The example in the slide creates a view that contains the employee number, last name, and
salary for each employee in department 80.
You can display the structure of the view by using the DESCRIBE command.
Guidelines
• The subquery that defines a view can contain complex SELECT syntax, including joins,
groups, and subqueries.
• If you do not specify a constraint name for the view created with the WITH CHECK
OPTION, the system assigns a default name in the SYS_Cn format.
• You can use the OR REPLACE option to change the definition of the view without
dropping and re-creating it, or regranting the object privileges previously granted on it.
Creating a View
• Create the EMPVU80 view, which contains details of the
employees in department 80:
• Describe the structure of the view by using the SQL*Plus
DESCRIBE command:
DESCRIBE empvu80;
CREATE VIEW empvu80
AS SELECT employee_id, last_name, salary
FROM employees
WHERE department_id = 80;

You can control the column names by including column aliases in the subquery.
The example in the slide creates a view containing the employee number (EMPLOYEE_ID)
with the alias ID_NUMBER, name (LAST_NAME) with the alias NAME, and annual salary
(SALARY) with the alias ANN_SALARY for every employee in department 50.
Alternatively, you can use an alias after the CREATE statement and before the SELECT
subquery. The number of aliases listed must match the number of expressions selected in the
subquery.
CREATE OR REPLACE VIEW salvu50 (ID_NUMBER, NAME, ANN_SALARY)
AS SELECT employee_id, last_name, salary*12
FROM employees
Creating a View
• Create a view by using column aliases in the subquery:
• Select the columns from this view by the given alias
names.
CREATE VIEW salvu50
AS SELECT employee_id ID_NUMBER, last_name NAME,
salary*12 ANN_SALARY
FROM employees

You can retrieve data from a view as you would from any table. You can display either the
contents of the entire view or just specific rows and columns.
SELECT *
FROM salvu50;
Retrieving Data from a View
…

With the OR REPLACE option, a view can be created even if one exists with this name already,
thus replacing the old version of the view for its owner. This means that the view can be
altered without dropping, re-creating, and regranting object privileges.
Note: When assigning column aliases in the CREATE OR REPLACE VIEW clause, remember
that the aliases are listed in the same order as the columns in the subquery.
Modifying a View
• Modify the EMPVU80 view by using a CREATE OR REPLACE
VIEW clause. Add an alias for each column name:
• Column aliases in the CREATE OR REPLACE VIEW clause
are listed in the same order as the columns in the
subquery.
CREATE OR REPLACE VIEW empvu80
(id_number, name, sal, department_id)
AS SELECT employee_id, first_name || ' '
|| last_name, salary, department_id
FROM employees

The example in the slide creates a complex view of department names, minimum salaries,
maximum salaries, and the average salaries by department. Note that alternative names have
been specified for the view. This is a requirement if any column of the view is derived from a
function or an expression.
You can view the structure of the view by using the DESCRIBE command. Display the
contents of the view by issuing a SELECT statement.
SELECT *
FROM dept_sum_vu;
Creating a Complex View
Create a complex view that contains group functions to display
values from two tables:
CREATE OR REPLACE VIEW dept_sum_vu
(name, minsal, maxsal, avgsal)
AS SELECT d.department_name, MIN(e.salary),
MAX(e.salary),AVG(e.salary)
FROM employees e JOIN departments d
ON (e.department_id = d.department_id)
GROUP BY d.department_name;

After your view is created, you can query the data dictionary view called USER_VIEWS to see
the name of the view and the view definition. The text of the SELECT statement that
constitutes your view is stored in a LONG column. The LENGTH column is the number of
characters in the SELECT statement. By default, when you select from a LONG column, only
the first 80 characters of the column’s value are displayed. To see more than 80 characters in
SQL*Plus, use the SET LONG command:
SET LONG 1000
In the examples in the slide:
1. The USER_VIEWS columns are displayed. Note that this is a partial listing.
2. The names of your views are retrieved
3. The SELECT statement for the EMP_DETAILS_VIEW is displayed from the dictionary
Data Access Using Views
When you access data by using a view, the Oracle Server performs the following operations:
• It retrieves the view definition from the data dictionary table USER_VIEWS.
• It checks access privileges for the view base table.
• It converts the view query into an equivalent operation on the underlying base table or
tables. That is, data is retrieved from, or an update is made to, the base tables.
View Information
DESCRIBE user_views
SELECT view_name FROM user_views;
SELECT text FROM user_views
WHERE view_name = 'EMP_DETAILS_VIEW';
1
2
3
…
…

• You can perform DML operations on data through a view if those operations follow
certain rules.
• You can remove a row from a view unless it contains any of the following:
- Group functions
- A GROUP BY clause
- The DISTINCT keyword
- The pseudocolumn ROWNUM keyword
Rules for Performing DML Operations on a View
• You can usually perform DML operations on
simple views.
• You cannot remove a row if the view contains the
following:
– Group functions
– A GROUP BY clause
– The DISTINCT keyword
– The pseudocolumn ROWNUM keyword

You can modify data through a view unless it contains any of the conditions mentioned in the
previous slide or columns defined by expressions (for example, SALARY * 12).
You cannot modify data in a view if it contains:
• Group functions
• A GROUP BY clause
• The DISTINCT keyword
• The pseudocolumn ROWNUM keyword
• Columns defined by expressions

You can add data through a view unless it contains any of the items listed in the slide. You
cannot add data to a view if the view contains NOT NULL columns without default values in the
base table. All the required values must be present in the view. Remember that you are
adding values directly to the underlying table through the view.
For more information, see the “CREATE VIEW” section in Oracle Database SQL Language
You cannot add data through a view if the view includes:
• Group functions
• A GROUP BY clause
• The DISTINCT keyword
• The pseudocolumn ROWNUM keyword
• Columns defined by expressions
• NOT NULL columns without default value in the base
tables that are not selected by the view

It is possible to perform referential integrity checks through views. You can also enforce
constraints at the database level. The view can be used to protect data integrity, but the use is
very limited.
The WITH CHECK OPTION clause specifies that INSERTs and UPDATEs performed through
the view cannot create rows that the view cannot select. Therefore, it enables integrity
constraints and data validation checks to be enforced on data being inserted or updated. If
there is an attempt to perform DML operations on rows that the view has not selected, an
error is displayed, along with the constraint name if that has been specified.
UPDATE empvu20
SET department_id = 10
WHERE employee_id = 201;
Error:
Note: No rows are updated because, if the department number were to change to 10, the
view would no longer be able to see that employee. With the WITH CHECK OPTION clause,
therefore, the view can see only the employees in department 20 and does not allow the
department number for those employees to be changed through the view.
SQL Error: ORA-01402: view WITH CHECK OPTION where-clause violation
01402. 00000 - "view WITH CHECK OPTION where-clause violation"
*Cause:
*Action:
Using the WITH CHECK OPTION Clause
• You can ensure that DML operations performed on the
view stay in the domain of the view by using the WITH
CHECK OPTION clause:
• Any attempt to INSERT a row with a department_id
other than 20 or to UPDATE the department number for any
row in the view fails because it violates the WITH CHECK
OPTION constraint.
AS SELECT *
FROM employees
WHERE department_id = 20
WITH CHECK OPTION CONSTRAINT empvu20_ck ;

You can ensure that no DML operations occur on your view by creating it with the WITH READ
ONLY option. The example in the next slide modifies the EMPVU10 view to prevent any DML
operations on the view.
Denying DML Operations
• You can ensure that no DML operations occur by adding
the WITH READ ONLY option to your view definition.
• Any attempt to perform a DML operation on any row in the
view results in an Oracle server error.

Any attempt to remove a row from a view with a read-only constraint results in an error:
DELETE FROM empvu10
WHERE employee_number = 200;
Similarly, any attempt to insert a row or modify a row using the view with a read-only
constraint results in the same error.
(employee_number, employee_name, job_title)
AS SELECT employee_id, last_name, job_id
FROM employees
WHERE department_id = 10
WITH READ ONLY ;
Denying DML Operations

You use the DROP VIEW statement to remove a view. The statement removes the view
definition from the database. However, dropping views has no effect on the tables on which
the view was based. Alternatively, views or other applications based on the deleted views
become invalid. Only the creator or a user with the DROP ANY VIEW privilege can remove a
view.
In the syntax, view is the name of the view.
Removing a View
You can remove a view without losing data because a view is
based on underlying tables in the database.
DROP VIEW view;
DROP VIEW empvu80;

Answer: a
Quiz
You cannot add data through a view if the view includes the
pseudocolumn ROWNUM keyword
a. True
b. False

In this lesson, you should have learned about views.
Summary
• Create, use, and remove views

The practice provides you with a variety of exercises in creating, using, querying data
dictionary views for view information, and removing views.
• Creating a simple view
• Creating a complex view
• Creating a view with a check constraint
• Attempting to modify data in the view
• Removing views

Managing Schema Objects

This lesson contains information about constraints and altering existing objects. You also
learn about external tables and the provision to name the index at the time of creating a
PRIMARY KEY constraint.
Objectives
• Manage constraints
• Create and use temporary tables
• Creating and use external tables

Lesson Agenda
• Managing constraints:
– Adding and dropping a constraint
– Enabling and disabling a constraint
– Deferring constraints
• Creating and using temporary tables
• Creating and using external tables

You can add a constraint for existing tables by using the ALTER TABLE statement with the
ADD clause.
In the syntax:
constraint Is the name of the constraint
type Is the constraint type
column Is the name of the column affected by the constraint
The constraint name syntax is optional, although recommended. If you do not name your
constraints, the system generates constraint names.
Guidelines
• You can add, drop, enable, or disable a constraint, but you cannot modify its structure.
• You can add a NOT NULL constraint to an existing column by using the MODIFY clause
of the ALTER TABLE statement.
Note: You can define a NOT NULL column only if the table is empty or if the column has a
value for every row.
Adding a Constraint Syntax
Use the ALTER TABLE statement to:
• Add or drop a constraint, but not to modify its structure
• Enable or disable constraints
• Add a NOT NULL constraint by using the MODIFY clause
ALTER TABLE <table_name>
ADD [CONSTRAINT <constraint_name>]
type (<column_name>);

The first example in the slide modifies the EMP2 table to add a PRIMARY KEY constraint on
the EMPLOYEE_ID column. Note that because no constraint name is provided, the constraint
is automatically named by the Oracle Server. The second example in the slide creates a
FOREIGN KEY constraint on the EMP2 table. The constraint ensures that a manager exists as
a valid employee in the EMP2 table.
ALTER TABLE emp2
MODIFY employee_id PRIMARY KEY;
Adding a Constraint
Add a FOREIGN KEY constraint to the EMP2 table indicating that
a manager must already exist as a valid employee in the EMP2
table.
ALTER TABLE emp2
ADD CONSTRAINT emp_mgr_fk
FOREIGN KEY(manager_id)
REFERENCES emp2(employee_id);

The drop_constraint_clause enables you to drop an integrity constraint from a
database.
To drop a constraint, you can identify the constraint name from the USER_CONSTRAINTS and
USER_CONS_COLUMNS data dictionary views. Then use the ALTER TABLE statement with the
DROP clause. The CASCADE option of the DROP clause causes any dependent constraints also
to be dropped.
Syntax
ALTER TABLE table
DROP PRIMARY KEY | UNIQUE (column) |
CONSTRAINT constraint [CASCADE];
In the syntax:
column Is the name of the column affected by the constraint
When you drop an integrity constraint, that constraint is no longer enforced by the Oracle
Server and is no longer available in the data dictionary.
Dropping a Constraint
• The drop_constraint_clause enables you to drop an
integrity constraint from a database.
• Remove the manager constraint from the EMP2 table:
• Remove the PRIMARY KEY constraint on the DEPT2 table
and drop the associated FOREIGN KEY constraint on the
EMP2.DEPARTMENT_ID column:
ALTER TABLE emp2
DROP CONSTRAINT emp_mgr_fk;
ALTER TABLE emp2
DROP PRIMARY KEY CASCADE;

/
You can also drop a constraint using an ONLINE keyword.
ALTER TABLE myemp2
DROP CONSTRAINT emp_id_pk ONLINE;
Use the ALTER TABLE statement with the DROP clause. The ONLINE option of the DROP
clause indicates that DML operations on the table are allowed while dropping the constraint.
Dropping a CONSTRAINT ONLINE
You can specify the ONLINE keyword to indicate that DML
operations on the table are allowed while dropping the
constraint.
ALTER TABLE myemp2
DROP CONSTRAINT emp_name_pk ONLINE;

ON DELETE
By using the ON DELETE clause, you can determine how Oracle Database handles referential
integrity if you remove a referenced primary or unique key value.
ON DELETE CASCADE
The ON DELETE CASCADE action allows parent key data that is referenced from the child
table to be deleted, but not updated. When data in the parent key is deleted, all the rows in
the child table that depend on the deleted parent key values are also deleted. To specify this
referential action, include the ON DELETE CASCADE option in the definition of the FOREIGN
KEY constraint.
ON DELETE SET NULL
When data in the parent key is deleted, the ON DELETE SET NULL action causes all the
rows in the child table that depend on the deleted parent key value to be converted to null.
If you omit this clause, Oracle does not allow you to delete referenced key values in the
parent table that have dependent rows in the child table.
ON DELETE Clause
• Use the ON DELETE CASCADE clause to delete child rows
when a parent key is deleted:
ALTER TABLE emp2 ADD CONSTRAINT emp_dt_fk
FOREIGN KEY (Department_id)
REFERENCES departments(department_id) ON DELETE CASCADE;
ALTER TABLE emp2 ADD CONSTRAINT emp_dt_fk
FOREIGN KEY (Department_id)
REFERENCES departments(department_id) ON DELETE SET NULL;
• Use the ON DELETE SET NULL clause to set the child
rows value to null when a parent key is deleted:

This statement illustrates the usage of the CASCADE CONSTRAINTS clause. Assume that the
TEST1 table is created as follows:
CREATE TABLE test1 (
col1_pk NUMBER PRIMARY KEY,
col2_fk NUMBER,
col1 NUMBER,
col2 NUMBER,
CONSTRAINT fk_constraint FOREIGN KEY (col2_fk) REFERENCES
test1,
CONSTRAINT ck1 CHECK (col1_pk > 0 and col1 > 0),
CONSTRAINT ck2 CHECK (col2_fk > 0));
An error is returned for the following statements:
ALTER TABLE test1 DROP (col1_pk); —col1_pk is a parent key.
ALTER TABLE test1 DROP (col1); —col1 is referenced by the multicolumn
constraint, ck1.
Cascading Constraints
• The CASCADE CONSTRAINTS clause is used along with
the DROP COLUMN clause.
• The CASCADE CONSTRAINTS clause drops all referential
integrity constraints that refer to the PRIMARY and UNIQUE
keys defined on the dropped columns.
• The CASCADE CONSTRAINTS clause also drops all
multicolumn constraints defined on the dropped columns.

Submitting the following statement drops the EMPLOYEE_ID column, the PRIMARY KEY
constraint, and any FOREIGN KEY constraints referencing the PRIMARY KEY constraint for the
EMP2 table:
ALTER TABLE emp2 DROP COLUMN employee_id CASCADE CONSTRAINTS;
If all columns referenced by the constraints defined on the dropped columns are also
dropped, CASCADE CONSTRAINTS is not required. For example, assuming that no other
referential constraints from other tables refer to the COL1_PK column, it is valid to submit the
following statement without the CASCADE CONSTRAINTS clause for the TEST1 table created
on the previous page:
ALTER TABLE test1 DROP (col1_pk, col2_fk, col1);
Cascading Constraints
Example:
ALTER TABLE emp2
DROP COLUMN employee_id CASCADE CONSTRAINTS;
ALTER TABLE test1
DROP (col1_pk, col2_fk, col1) CASCADE CONSTRAINTS;

• Enabling a PRIMARY KEY constraint that was disabled with the CASCADE option does not
enable any FOREIGN KEYs that are dependent on the PRIMARY KEY.
• To enable a UNIQUE or PRIMARY KEY constraint, you must have the privileges necessary
to create an index on the table.

When you rename a table column, the new name must not conflict with the name of any
existing column in the table. You cannot use any other clauses in conjunction with the
RENAME COLUMN clause.
The slide examples use the marketing table with the PRIMARY KEY mktg_pk defined on
the id column.
CREATE TABLE marketing (team_id NUMBER(10),
target VARCHAR2(50),
CONSTRAINT mktg_pk PRIMARY KEY(team_id));
Example a shows that the id column of the marketing table is renamed mktg_id. Example b
shows that mktg_pk is renamed new_mktg_pk.
When you rename any existing constraint for a table, the new name must not conflict with any
of your existing constraint names. You can use the RENAME CONSTRAINT clause to rename
system-generated constraint names.
Renaming Table Columns and Constraints
• Use the RENAME COLUMN clause of the ALTER TABLE
statement to rename table columns.
• Use the RENAME CONSTRAINT clause of the ALTER TABLE
statement to rename any existing constraint for a table.
ALTER TABLE marketing RENAME COLUMN team_id
TO id;
ALTER TABLE marketing RENAME CONSTRAINT mktg_pk
TO new_mktg_pk;
a
b

You can disable a constraint, without dropping it or re-creating it, by using the ALTER TABLE
statement with the DISABLE clause.
Syntax
ALTER TABLE table
DISABLE CONSTRAINT constraint [CASCADE];
In the syntax:
Guidelines
• You can use the DISABLE clause in both the CREATE TABLE statement and the ALTER
TABLE statement.
• The CASCADE clause disables dependent integrity constraints.
• Disabling a UNIQUE or PRIMARY KEY constraint removes the unique index.
Disabling Constraints
• Execute the DISABLE clause of the ALTER TABLE
statement to deactivate an integrity constraint.
• Apply the CASCADE option to disable dependent integrity
constraints.
ALTER TABLE emp2
DISABLE CONSTRAINT emp_dt_fk;

You can enable a constraint without dropping it or re-creating it by using the ALTER TABLE
statement with the ENABLE clause.
Syntax
ALTER TABLE table
ENABLE CONSTRAINT constraint;
In the syntax:
Guidelines
• If you enable a constraint, that constraint applies to all the data in the table. All the data
in the table must comply with the constraint.
• If you enable a UNIQUE key or a PRIMARY KEY constraint, a UNIQUE or PRIMARY KEY
index is created automatically. If an index already exists, it can be used by these keys.
• You can use the ENABLE clause in both the CREATE TABLE statement and the ALTER
TABLE statement.
Enabling Constraints
• Activate an integrity constraint that is currently disabled in
the table definition by using the ENABLE clause.
• A UNIQUE index is automatically created if you enable a
UNIQUE key or a PRIMARY KEY constraint.
ALTER TABLE emp2
ENABLE CONSTRAINT emp_dt_fk;

You can defer checking constraints for validity until the end of the transaction. A constraint is
deferred if the system does not check whether the constraint is satisfied, until a COMMIT
statement is submitted. If a deferred constraint is violated, the database returns an error and
the transaction is not committed and it is rolled back. If a constraint is immediate (not
deferred), it is checked at the end of each statement. If it is violated, the statement is rolled
back immediately. If a constraint causes an action (for example, DELETE CASCADE), that
action is always taken as part of the statement that caused it, whether the constraint is
deferred or immediate. Use the SET CONSTRAINTS statement to specify, for a particular
transaction, whether a deferrable constraint is checked following each data manipulation
language (DML) statement or when the transaction is committed. To create deferrable
constraints, you must create a nonunique index for that constraint.
You can define constraints as either deferrable or NOT DEFERRABLE (default), and either
initially deferred or INITIALLY IMMEDIATE (default). These attributes can be different for
each constraint.
Usage scenario: Company policy dictates that department number 40 should be changed to
45. Changing the DEPARTMENT_ID column affects employees assigned to this department.
Therefore, you make the PRIMARY KEY and FOREIGN KEYs deferrable and initially deferred.
You update both department and employee information, and at the time of commit, all the
rows are validated.
Deferring Constraints
Constraints can have the following attributes:
• DEFERRABLE or NOT DEFERRABLE
• INITIALLY DEFERRED or INITIALLY IMMEDIATE
ALTER TABLE dept2
ADD CONSTRAINT dept2_id_pk
PRIMARY KEY (department_id)
DEFERRABLE INITIALLY DEFERRED;
ALTER SESSION
SET CONSTRAINTS= IMMEDIATE;
SET CONSTRAINTS dept2_id_pk IMMEDIATE;
Deferring constraint on
creation
Changing all constraints for a
session
Changing a specific
constraint attribute

A constraint that is defined as deferrable can be specified as either INITIALLY DEFERRED
or INITIALLY IMMEDIATE. The INITIALLY IMMEDIATE clause is the default.
In the slide example:
• The sal_ck constraint is created as DEFERRABLE INITIALLY IMMEDIATE
• The bonus_ck constraint is created as DEFERRABLE INITIALLY DEFERRED
After creating the emp_new_sal table, as shown in the slide, you attempt to insert values into
the table and observe the results. When both the sal_ck and bonus_ck constraints are
satisfied, the rows are inserted without an error.
Example 1: Insert a row that violates sal_ck. In the CREATE TABLE statement, sal_ck is
specified as an initially immediate constraint. This means that the constraint is verified
immediately after the INSERT statement and you observe an error.
INSERT INTO emp_new_sal VALUES(90,5);
Example 2: Insert a row that violates bonus_ck. In the CREATE TABLE statement,
bonus_ck is specified as deferrable and also initially deferred. Therefore, the constraint is
not verified until you COMMIT or set the constraint state back to immediate.
Difference Between INITIALLY DEFERRED
and INITIALLY IMMEDIATE
INITIALLY DEFERRED Waits until the transaction ends to
check the constraint
INITIALLY IMMEDIATE Checks the constraint at the end of
the statement execution
CREATE TABLE emp_new_sal (salary NUMBER
CONSTRAINT sal_ck
CHECK (salary > 100)
DEFERRABLE INITIALLY IMMEDIATE,
bonus NUMBER
CONSTRAINT bonus_ck
CHECK (bonus > 0 )
DEFERRABLE INITIALLY DEFERRED );

INSERT INTO emp_new_sal VALUES(110, -1);
The row insertion is successful. But you observe an error when you commit the transaction.
COMMIT;
The commit failed due to constraint violation. Therefore, at this point, the transaction is rolled
back by the database.
Example 3: Set the DEFERRED status to all constraints that can be deferred. Note that you can
also set the DEFERRED status to a single constraint if required.
SET CONSTRAINTS ALL DEFERRED;
Now, if you attempt to insert a row that violates the sal_ck constraint, the statement is
executed successfully.
INSERT INTO emp_new_sal VALUES(90,5);
However, you observe an error when you commit the transaction. The transaction fails and is
rolled back. This is because both the constraints are checked upon COMMIT.
COMMIT;
Example 4: Set the IMMEDIATE status to both the constraints that were set as DEFERRED in
the previous example.
SET CONSTRAINTS ALL IMMEDIATE;
You observe an error if you attempt to insert a row that violates either sal_ck or bonus_ck.
INSERT INTO emp_new_sal VALUES(110, -1);
Note: If you create a table without specifying constraint deferability, the constraint is checked
immediately at the end of each statement. For example, with the CREATE TABLE statement of
the newemp_details table, if you do not specify the newemp_det_pk constraint deferability,
the constraint is checked immediately.
CREATE TABLE newemp_details(emp_id NUMBER, emp_name
VARCHAR2(20),
CONSTRAINT newemp_det_pk PRIMARY KEY(emp_id));
When you attempt to defer the newemp_det_pk constraint that is not deferrable, you observe
the following error:
SET CONSTRAINT newemp_det_pk DEFERRED;

Oracle Database provides a feature for dropping tables. When you drop a table, the database
does not immediately release the space associated with the table. Rather, the database
renames the table and places it in a recycle bin, where it can later be recovered with the
FLASHBACK TABLE statement if you find that you dropped the table in error. If you want to
immediately release the space associated with the table at the time you issue the DROP
TABLE statement, include the PURGE clause as shown in the statement in the slide.
Specify PURGE only if you want to drop the table and release the space associated with it in a
single step. If you specify PURGE, the database does not place the table and its dependent
objects into the recycle bin.
Using this clause is equivalent to first dropping the table and then purging it from the recycle
bin. This clause saves you one step in the process. It also provides enhanced security if you
want to prevent sensitive material from appearing in the recycle bin.
DROP TABLE … PURGE
DROP TABLE emp_new_sal PURGE;

Lesson Agenda

A temporary table is a table that holds data that exists only for the duration of a transaction or
session. Data in a temporary table is private to the session, which means that each session
can see and modify only its own data.
Temporary tables are useful in applications where a result set must be buffered. For example,
a shopping cart in an online application can be a temporary table. Each item is represented by
a row in the temporary table. While you are shopping in an online store, you can keep on
adding or removing items from your cart. During the session, this cart data is private. After you
finalize your shopping and make the payments, the application moves the row for the chosen
cart to a permanent table. At the end of the session, the data in the temporary table is
automatically dropped.
Because temporary tables are statically defined, you can create indexes for them. Indexes
created on temporary tables are also temporary. The data in the index has the same session
or transaction scope as the data in the temporary table. You can also create a view or trigger
on a temporary table.
Temporary Tables
When
session/transaction
completes

To create a temporary table, you can use the following command:
CREATE GLOBAL TEMPORARY TABLE tablename
ON COMMIT [PRESERVE | DELETE] ROWS
By associating one of the following settings with the ON COMMIT clause, you can decide
whether the data in the temporary table is transaction-specific (default) or session-specific.
1. DELETE ROWS: As shown in example 1 in the slide, the DELETE ROWS setting creates a
temporary table that is transaction-specific. A session becomes bound to the temporary
table with a transaction’s first insert into the table. The binding goes away at the end of
the transaction. The database truncates the table (delete all rows) after each commit.
2. PRESERVE ROWS: As shown in example 2 in the slide, the PRESERVE ROWS setting
creates a temporary table that is session-specific. Each sales representative session
can store its own sales data for the day in the table. When a salesperson performs first
insert on the today_sales table, his or her session gets bound to the today_sales
table. This binding goes away at the end of the session or by issuing a TRUNCATE of the
table in the session. The database truncates the table when you terminate the session.
When you create a temporary table in an Oracle database, you create a static table definition.
Like permanent tables, temporary tables are defined in the data dictionary. However,
temporary tables and their indexes do not automatically allocate a segment when created.
Instead, temporary segments are allocated when data is first inserted. Until data is loaded in a
session, the table appears empty.
Creating a Temporary Table
CREATE GLOBAL TEMPORARY TABLE cart(n NUMBER,d DATE)
ON COMMIT DELETE ROWS;
CREATE GLOBAL TEMPORARY TABLE today_sales
ON COMMIT PRESERVE ROWS AS
SELECT * FROM orders
WHERE order_date = SYSDATE;
1
2

Lesson Agenda

An external table is a read-only table whose metadata is stored in the database but whose
data is stored outside the database. This external table definition can be thought of as a view
that is used for running any SQL query against external data without requiring that the
external data first be loaded into the database. The external table data can be queried and
joined directly and in parallel without requiring that the external data first be loaded in the
database. You can use SQL, PL/SQL, and Java to query the data in an external table.
The main difference between external tables and regular tables is that externally organized
tables are read-only. No data manipulation language (DML) operations are possible, and no
indexes can be created on them. However, you can create an external table, and thus unload
data, by using the CREATE TABLE AS SELECT command.
The Oracle Server provides two major access drivers for external tables. One, the loader
access driver (or ORACLE_LOADER) is used for reading data from external files whose format
can be interpreted by the SQL*Loader utility. Note that not all SQL*Loader functionality is
supported with external tables. The ORACLE_DATAPUMP access driver can be used to both
import and export data by using a platform-independent format. The ORACLE_DATAPUMP
access driver writes rows from a SELECT statement to be loaded into an external table as part
of a CREATE TABLE ...ORGANIZATION EXTERNAL...AS SELECT statement. You can
then use SELECT to read data out of that data file. You can also create an external table
definition on another system and use that data file. This allows data to be moved between
Oracle databases.
External Tables

Use the CREATE DIRECTORY statement to create a directory object. A directory object
specifies an alias for a directory on the server’s file system where an external data source
resides. You can use directory names when referring to an external data source, rather than
hard code the operating system path name, for greater file management flexibility.
You must have CREATE ANY DIRECTORY system privileges to create directories. When you
create a directory, you are automatically granted the READ and WRITE object privileges and
can grant READ and WRITE privileges to other users and roles. The DBA can also grant these
privileges to other users and roles.
A user needs READ privileges for all directories used in external tables to be accessed and
WRITE privileges for the log, bad, and discard file locations being used.
In addition, a WRITE privilege is necessary when the external table framework is being used
to unload data.
Oracle also provides the ORACLE_DATAPUMP type, with which you can unload data (that is,
read data from a table in the database and insert it into an external table) and then reload it
into an Oracle database. This is a one-time operation that can be done when the table is
created. After the creation and initial population is done, you cannot update, insert, or delete
any rows.
Creating a Directory for the External Table
Create a DIRECTORY object that corresponds to the directory
on the file system where the external data source resides.
CREATE OR REPLACE DIRECTORY emp_dir
AS '/…/emp_dir';
GRANT READ ON DIRECTORY emp_dir TO ora_21;

Syntax
CREATE [OR REPLACE] DIRECTORY AS 'path_name';
In the syntax:
OR REPLACE Specify OR REPLACE to re-create the directory database
object if it already exists. You can use this clause to change
the definition of an existing directory without dropping, re-creating,
and regranting database object privileges previously granted
on the directory. Users who were previously granted privileges
on a redefined directory can continue to access the directory
without requiring that the privileges be regranted.
directory Specify the name of the directory object to be created. The
maximum length of the directory name is 30 bytes. You
cannot qualify a directory object with a schema name.
'path_name' Specify the full path name of the operating system directory
to be accessed. The path name is case-sensitive.

You create external tables by using the ORGANIZATION EXTERNAL clause of the CREATE
TABLE statement. You are not, in fact, creating a table. Rather, you are creating metadata in
the data dictionary that you can use to access external data. You use the ORGANIZATION
clause to specify the order in which the data rows of the table are stored. By specifying
EXTERNAL in the ORGANIZATION clause, you indicate that the table is a read-only table
located outside the database. Note that the external files must already exist outside the
database.
TYPE <access_driver_type> indicates the access driver of the external table. The
access driver is the application programming interface (API) that interprets the external data
for the database. If you do not specify TYPE, Oracle uses the default access driver,
ORACLE_LOADER. The other option is ORACLE_DATAPUMP.
You use the DEFAULT DIRECTORY clause to specify one or more Oracle database directory
objects that correspond to directories on the file system where the external data sources may
reside.
The optional ACCESS PARAMETERS clause enables you to assign values to the parameters of
the specific access driver for this external table.
Creating an External Table
CREATE TABLE <table_name>
( <col_name> <datatype>, … )
ORGANIZATION EXTERNAL
(TYPE <access_driver_type>
DEFAULT DIRECTORY <directory_name>
ACCESS PARAMETERS
(… ) )
LOCATION ('<location_specifier>')
REJECT LIMIT [0 | <number> | UNLIMITED];

Use the LOCATION clause to specify one external locator for each external data source.
Usually, <location_specifier> is a file, but it need not be.
The REJECT LIMIT clause enables you to specify how many conversion errors can occur
during a query of the external data before an Oracle error is returned and the query is aborted.
The default value is 0.
The syntax for using the ORACLE_DATAPUMP access driver is as follows:
CREATE TABLE extract_emps
ORGANIZATION EXTERNAL (TYPE ORACLE_DATAPUMP
DEFAULT DIRECTORY …
ACCESS PARAMETERS (… )
LOCATION (…)
PARALLEL 4
REJECT LIMIT UNLIMITED
AS
SELECT * FROM …;

Assume that there is a flat file that has records in the following format:
10,jones,11-Dec-1934
20,smith,12-Jun-1972
Records are delimited by new lines, and the fields are all terminated by a comma (,). The
name of the file is /emp_dir/emp.dat.
To convert this file as the data source for an external table, whose metadata will reside in the
database, you must perform the following steps:
1. Create a directory object, emp_dir, as follows:
CREATE DIRECTORY emp_dir AS '/emp_dir' ;
2. Run the CREATE TABLE command shown in the slide.
The example in the slide illustrates the table specification to create an external table for the
file:
/emp_dir/emp.dat
by Using ORACLE_LOADER
CREATE TABLE oldemp (
fname char(25), lname CHAR(25))
(TYPE ORACLE_LOADER
DEFAULT DIRECTORY emp_dir
ACCESS PARAMETERS
(RECORDS DELIMITED BY NEWLINE
NOBADFILE
NOLOGFILE
FIELDS TERMINATED BY ','
(fname POSITION ( 1:20) CHAR,
lname POSITION (22:41) CHAR))
LOCATION ('emp.dat'))
PARALLEL 5
REJECT LIMIT 200;

In the example, the TYPE specification is given only to illustrate its use. ORACLE_LOADER is the
default access driver if not specified. The ACCESS PARAMETERS option provides values to
parameters of the specific access driver, which are interpreted by the access driver, not by the
Oracle Server.
The PARALLEL clause enables five parallel execution servers to simultaneously scan the
external data sources (files) when executing the INSERT INTO TABLE statement. For example,
if PARALLEL=5 were specified, more than one parallel execution server can be working on a
data source. Because external tables can be very large, for performance reasons, it is advisable
to specify the PARALLEL clause, or a parallel hint for the query.
The REJECT LIMIT clause specifies that if more than 200 conversion errors occur during a
query of the external data, the query must be aborted and an error must be returned. These
conversion errors can arise when the access driver tries to transform the data in the data file to
match the external table definition.
After the CREATE TABLE command executes successfully, the OLDEMP external table can be
described and queried in the same way as a relational table.

An external table does not describe any data that is stored in the database. It does not
describe how data is stored in the external source. Instead, it describes how the external table
layer must present the data to the server. It is the responsibility of the access driver and the
external table layer to do the necessary transformations required on the data in the data file
so that it matches the external table definition.
When the database server accesses data in an external source, it calls the appropriate
access driver to get the data from an external source in a form that the database server
expects.
It is important to remember that the description of the data in the data source is separate from
the definition of the external table. The source file can contain more or fewer fields than there
are columns in the table. Also, the data types for fields in the data source can be different
from the columns in the table. The access driver takes care of ensuring that the data from the
data source is processed so that it matches the definition of the external table.
Querying External Tables
SELECT *
FROM oldemp
emp.dat
OLDEMP

You can perform the unload and reload operations with external tables by using the
ORACLE_DATAPUMP access driver.
Note: In the context of external tables, loading data refers to the act of data being read from
an external table and loaded into a table in the database. Unloading data refers to the act of
reading data from a table and inserting it into an external table.
The example in the slide illustrates the table specification to create an external table by using
the ORACLE_DATAPUMP access driver. Data is then populated into the two files: emp1.exp
and emp2.exp.
To populate data read from the EMPLOYEES table into an external table, you must perform the
following steps:
1. Create a directory object, emp_dir, as follows:
CREATE DIRECTORY emp_dir AS '/emp_dir' ;
2. Run the CREATE TABLE command shown in the slide.
Note: The emp_dir directory is the same as created in the previous example of using
ORACLE_LOADER.
You can query the external table by executing the following code:
SELECT * FROM emp_ext;
by Using ORACLE_DATAPUMP: Example
CREATE TABLE emp_ext
(employee_id, first_name, last_name)
(
TYPE ORACLE_DATAPUMP
DEFAULT DIRECTORY emp_dir
LOCATION
('emp1.exp','emp2.exp')
)
PARALLEL
AS
SELECT employee_id, first_name, last_name
FROM employees;

Answer: b
Quiz
A FOREIGN KEY constraint enforces the following action:
When the data in the parent key is deleted, all the rows in the
child table that depend on the deleted parent key values are
also deleted.
a. True
b. False

In this lesson, you learned how to perform the following tasks for schema object management:
• Alter tables to add or modify columns or constraints.
• Use the ORGANIZATION EXTERNAL clause of the CREATE TABLE statement to create
an external table. An external table is a read-only table whose metadata is stored in the
database but whose data is stored outside the database.
• Use external tables to query data without first loading it into the database.
Summary
• Manage constraints
• Create and use temporary tables
• Create and use external tables

In this practice, you use the ALTER TABLE command to add, drop and defer constraints. You
create external tables.
• Adding and dropping constraints
• Deferring constraints
• Creating external tables

Retrieving Data by Using Subqueries

In this lesson, you learn how to write multiple-column subqueries and subqueries in the FROM
clause of a SELECT statement. You also learn how to solve problems by using scalar,
correlated subqueries and the WITH clause.
Objectives
• Write a multiple-column subquery
• Use scalar subqueries in SQL
• Solve problems with correlated subqueries
• Update and delete rows by using correlated subqueries
• Use the EXISTS and NOT EXISTS operators
• Use the WITH clause

Lesson Agenda
• Retrieving data by using a subquery as a source
• Writing a multiple-column subquery
• Using scalar subqueries in SQL
• Solving problems with correlated subqueries
• Using the EXISTS and NOT EXISTS operators
• Using the WITH clause

You can use a subquery in the FROM clause of a SELECT statement, which is very similar to
how views are used. A subquery in the FROM clause of a SELECT statement is also called an
inline view. A subquery in the FROM clause of a SELECT statement defines a data source for
that particular SELECT statement, and only that SELECT statement. As with a database view,
the SELECT statement in the subquery can be as simple or as complex as you like.
When a database view is created, the associated SELECT statement is stored in the data
dictionary. In situations where you do not have the necessary privileges to create database
views, or when you would like to test the suitability of a SELECT statement to become a view,
you can use an inline view.
With inline views, you can have all the code needed to support the query in one place. This
means that you can avoid the complexity of creating a separate database view. The example
in the slide shows how to use an inline view to display the department name and the city in
Europe. The subquery in the FROM clause fetches the location ID, city name, and the country
by joining three different tables. The output of the inner query is considered as a table for the
outer query. The inner query is similar to that of a database view but does not have any
physical name.
SELECT department_name, city
FROM departments
NATURAL JOIN (SELECT l.location_id, l.city, l.country_id
FROM locations l
JOIN countries c
ON(l.country_id = c.country_id)
JOIN regions USING(region_id)
WHERE region_name = 'Europe');
Retrieving Data by Using a Subquery as a Source

You can display the same output as in the example in the slide by performing the following
two steps:
1. Create a database view:
CREATE OR REPLACE VIEW european_cities
AS
SELECT l.location_id, l.city, l.country_id
FROM locations l
JOIN countries c
WHERE region_name = 'Europe';
2. Join the EUROPEAN_CITIES view with the DEPARTMENTS table:
SELECT department_name, city
FROM departments
NATURAL JOIN european_cities;
Note: You learned how to create database views in the lesson titled Creating Views.

Lesson Agenda

So far, you have written single-row subqueries and multiple-row subqueries where only one
column is returned by the inner SELECT statement and this is used to evaluate the expression
in the parent SELECT statement. If you want to compare two or more columns, you must write
a compound WHERE clause using logical operators. Using multiple-column subqueries, you
can combine duplicate WHERE conditions into a single WHERE clause.
Syntax
SELECT column, column, ...
FROM table
WHERE (column, column, ...) IN
(SELECT column, column, ...
FROM table
WHERE condition);
The graphic in the slide illustrates that the values of MANAGER_ID and DEPARTMENT_ID from
the main query are being compared with the MANAGER_ID and DEPARTMENT_ID values
retrieved by the subquery. Because the number of columns that are being compared is more
than one, the example qualifies as a multiple-column subquery.
Note: Before you run the examples in the next few slides, you need to create the empl_demo
table and populate data into it by using the lab_06_insert_empdata.sql file.
Multiple-Column Subqueries
Main query
WHERE (MANAGER_ID, DEPARTMENT_ID) IN
Subquery
100 90
102 60
124 50
Each row of the main query is compared to values from a
multiple-row and multiple-column subquery.

Pairwise Versus Nonpairwise Comparisons
Multiple-column comparisons involving subqueries can be nonpairwise comparisons or
pairwise comparisons. If you consider the example “Display the details of the employees who
work in the same department, and have the same manager, as ‘Daniel’?,” you get the correct
result with the following statement:
SELECT first_name, last_name, manager_id, department_id
FROM empl_demo
WHERE manager_id IN (SELECT manager_id
FROM empl_demo
WHERE first_name = 'Daniel')
AND department_id IN (SELECT department_id
FROM empl_demo
WHERE first_name = 'Daniel');
There is only one “Daniel” in the EMPL_DEMO table (Daniel Faviet, who is managed by
employee 108 and works in department 100). However, if the subqueries return more than
one row, the result might not be correct. For example, if you run the same query but substitute
“John” for “Daniel,” you get an incorrect result. This is because the combination of
department_id and manager_id is important. To get the correct result for this query, you
need a pairwise comparison.
Column Comparisons
Multiple-column comparisons involving subqueries can be:
• Nonpairwise comparisons
• Pairwise comparisons

The example in the slide compares the combination of values in the MANAGER_ID column
and the DEPARTMENT_ID column of each row in the EMPL_DEMO table with the values in the
MANAGER_ID column and the DEPARTMENT_ID column for the employees with the
FIRST_NAME of “John.” First, the subquery to retrieve the MANAGER_ID and
DEPARTMENT_ID values for the employees with the FIRST_NAME of “John” is executed. This
subquery returns the following:
Pairwise Comparison Subquery
Display the details of the employees who are managed by the
same manager and work in the same department as
employees with the first name of “John.”
SELECT employee_id, manager_id, department_id
FROM empl_demo
WHERE (manager_id, department_id) IN
(SELECT manager_id, department_id
FROM empl_demo
WHERE first_name = 'John')
AND first_name <> 'John';

These values are compared with the MANAGER_ID column and the DEPARTMENT_ID column of
each row in the EMPL_DEMO table. If the combination matches, the row is displayed. In the
output, the records of the employees with the FIRST_NAME of “John” will not be displayed. The
following is the output of the query in the slide:

The example shows a nonpairwise comparison of the columns. First, the subquery to retrieve
the MANAGER_ID values for the employees with the FIRST_NAME of “John” is executed.
Similarly, the second subquery to retrieve the DEPARTMENT_ID values for the employees with
the FIRST_NAME of “John” is executed. The retrieved values of the MANAGER_ID and
DEPARTMENT_ID columns are compared with the MANAGER_ID and DEPARTMENT_ID
columns for each row in the EMPL_DEMO table. If the MANAGER_ID column of the row in the
EMPL_DEMO table matches with any of the values of MANAGER_ID retrieved by the inner
subquery, and if the DEPARTMENT_ID column of the row in the EMPL_DEMO table matches
with any of the values of DEPARTMENT_ID retrieved by the second subquery, the record is
displayed.
Nonpairwise Comparison Subquery
Display the details of the employees who are managed by the
same manager as the employees with the first name of “John”
and work in the same department as the employees with the
first name of “John.”
SELECT employee_id, manager_id, department_id
FROM empl_demo
WHERE manager_id IN
(SELECT manager_id
FROM empl_demo
AND department_id IN
(SELECT department_id
FROM empl_demo
AND first_name <> 'John';

The following is the output of the query in the slide:
This query retrieves more rows than the pairwise comparison (those with the combination of
manager_id=100 and department_id=50 or 80, although no employee named “John” has
such a combination).

Lesson Agenda

A subquery that returns exactly one column value from one row is also referred to as a scalar
subquery. Multiple-column subqueries that are written to compare two or more columns, using
a compound WHERE clause and logical operators, do not qualify as scalar subqueries.
The value of the scalar subquery expression is the value of the select list item of the
subquery. If the subquery returns 0 rows, the value of the scalar subquery expression is
NULL. If the subquery returns more than one row, the Oracle Server returns an error. The
Oracle Server has always supported the usage of a scalar subquery in a SELECT statement.
You can use scalar subqueries in:
• The condition and expression part of DECODE and CASE
• All clauses of SELECT except GROUP BY
• The SET clause and WHERE clause of an UPDATE statement
However, scalar subqueries are not valid expressions in the following places:
• As default values for columns and hash expressions for clusters
• In the RETURNING clause of data manipulation language (DML) statements
• As the basis of a function-based index
• In GROUP BY clauses, CHECK constraints
• In CONNECT BY clauses
• In statements that are unrelated to queries, such as CREATE PROFILE
Scalar Subquery Expressions
• A scalar subquery expression is a subquery that
returns exactly one column value from one row.
• Scalar subqueries can be used in:
– The condition and expression part of DECODE and CASE
– All clauses of SELECT except GROUP BY
– The SET clause and WHERE clause of an UPDATE statement

…
…
Scalar Subqueries: Examples
• Scalar subqueries in CASE expressions:
• Scalar subqueries in the ORDER BY clause:
SELECT employee_id, last_name,
(CASE
WHEN department_id =
(SELECT department_id
FROM departments
WHERE location_id = 1800)
THEN 'Canada' ELSE 'USA' END) location
FROM employees;
SELECT employee_id, last_name
FROM employees e
ORDER BY (SELECT department_name
FROM departments d
WHERE e.department_id = d.department_id);
20

The second example in the slide demonstrates that scalar subqueries can be used in the ORDER
BY clause. The example orders the output based on the DEPARTMENT_NAME by matching the
DEPARTMENT_ID from the EMPLOYEES table with the DEPARTMENT_ID from the
DEPARTMENTS table. This comparison is done in a scalar subquery in the ORDER BY clause.
The following is the result of the second example:
The second example uses a correlated subquery. In a correlated subquery, the subquery
references a column from a table referred to in the parent statement. Correlated subqueries are
explained later in this lesson.
…

Lesson Agenda

The Oracle Server performs a correlated subquery when the subquery references a column
from a table referred to in the parent statement. A correlated subquery is evaluated once for
each row processed by the parent statement. The parent statement can be a SELECT,
UPDATE, or DELETE statement.
Nested Subqueries Versus Correlated Subqueries
With a normal nested subquery, the inner SELECT query runs first and executes once,
returning values to be used by the main query. A correlated subquery, however, executes
once for each candidate row considered by the outer query. That is, the inner query is driven
by the outer query.
Nested Subquery Execution
• The inner query executes first and finds a value.
• The outer query executes once, using the value from the inner query.
Correlated Subquery Execution
• Get a candidate row (fetched by the outer query).
• Execute the inner query by using the value of the candidate row.
• Use the values resulting from the inner query to qualify or disqualify the candidate.
• Repeat until no candidate row remains.
Correlated Subqueries
Correlated subqueries are used for row-by-row processing.
Each subquery is executed once for every row of the outer
query.
GET
candidate row from outer query
EXECUTE
inner query using candidate row value
USE
values from inner query to qualify or
disqualify candidate row

A correlated subquery is one way of reading every row in a table and comparing values in
each row against related data. It is used whenever a subquery must return a different result or
set of results for each candidate row considered by the main query. That is, you use a
correlated subquery to answer a multipart question whose answer depends on the value in
each row processed by the parent statement.
from a table in the parent query.
Note: You can use the ANY and ALL operators in a correlated subquery.
Correlated Subqueries
The subquery references a column from a table in the parent
query.
SELECT column1, column2, ...
FROM table1
WHERE column1 operator
(SELECT column1, column2
FROM table2
WHERE expr1 =
.expr2);
Outer_table
Outer_table

The example in the slide finds which employees earn more than the average salary of their
department. In this case, the correlated subquery specifically computes the average salary for
each department.
Because both the outer query and inner query use the EMPLOYEES table in the FROM clause,
an alias is given to EMPLOYEES in the outer SELECT statement for clarity. The alias makes the
entire SELECT statement more readable. Without the alias, the query would not work properly
because the inner statement would not be able to distinguish the inner table column from the
outer table column.
SELECT last_name, salary, department_id
FROM employees outer_table
WHERE salary >
(SELECT AVG(salary)
FROM employees inner_table
WHERE inner_table.department_id =
outer_table.department_id);
Using Correlated Subqueries
Find all employees who earn more than the average salary in
their department.
Each time a row from
the outer query
is processed, the
inner query is
evaluated.

The example in the slide displays the details of those employees who have changed jobs at
least twice. The Oracle Server evaluates a correlated subquery as follows:
1. Select a row from the table specified in the outer query. This will be the current candidate
row.
2. Store the value of the column referenced in the subquery from this candidate row. (In the
example in the slide, the column referenced in the subquery is E.EMPLOYEE_ID.)
3. Perform the subquery with its condition referencing the value from the outer query’s
candidate row. (In the example in the slide, the COUNT(*) group function is evaluated
based on the value of the E.EMPLOYEE_ID column obtained in step 2.)
4. Evaluate the WHERE clause of the outer query on the basis of results of the subquery
performed in step 3. This determines whether the candidate row is selected for output. (In
the example, the number of times an employee has changed jobs, evaluated by the
subquery, is compared with 2 in the WHERE clause of the outer query. If the condition is
satisfied, that employee record is displayed.)
5. Repeat the procedure for the next candidate row of the table, and so on, until all the rows
in the table have been processed.
The correlation is established by using an element from the outer query in the subquery. In
this example, you compare EMPLOYEE_ID from the table in the subquery with EMPLOYEE_ID
from the table in the outer query.
Using Correlated Subqueries
Display details of those employees who have changed
jobs at least twice.
SELECT e.employee_id, last_name,e.job_id
FROM employees e
WHERE 2 <= (SELECT COUNT(*)
FROM job_history
WHERE employee_id = e.employee_id);

Lesson Agenda

With nesting SELECT statements, all logical operators are valid. In addition, you can use the
EXISTS operator. This operator is frequently used with correlated subqueries to test whether
a value retrieved by the outer query exists in the results set of the values retrieved by the
inner query. If the subquery returns at least one row, the operator returns TRUE. If the value
does not exist, it returns FALSE. Accordingly, NOT EXISTS tests whether a value retrieved by
the outer query is not a part of the results set of the values retrieved by the inner query.
Using the EXISTS Operator
• The EXISTS operator tests for existence of rows in the
results set of the subquery.
• If a subquery row value is found:
– The search does not continue in the inner query
– The condition is flagged TRUE
• If a subquery row value is not found:
– The condition is flagged FALSE
– The search continues in the inner query

The EXISTS operator ensures that the search in the inner query does not continue when at
least one match is found for the manager and employee number by the condition:
WHERE manager_id = outer.employee_id.
Note that the inner SELECT query does not need to return a specific value, so a constant can
be selected.
SELECT employee_id, last_name, job_id, department_id
FROM employees outer
WHERE EXISTS ( SELECT 'X'
FROM employees
WHERE manager_id =
outer.employee_id);
Using the EXISTS Operator
…

Using the NOT EXISTS Operator
Alternative Solution
A NOT IN construct can be used as an alternative for a NOT EXISTS operator, as shown in
the following example:
SELECT department_id, department_name
FROM departments
WHERE department_id NOT IN (SELECT department_id
FROM employees);
However, NOT IN evaluates to FALSE if any member of the set is a NULL value. Therefore,
your query will not return any rows even if there are rows in the departments table that
satisfy the WHERE condition.
SELECT department_id, department_name
FROM departments d
WHERE NOT EXISTS (SELECT 'X'
FROM employees
WHERE department_id = d.department_id);
Find All Departments
That Do Not Have Any Employees
…

Lesson Agenda

Using the WITH clause, you can define a query block before using it in a query. The WITH
clause (formally known as subquery_factoring_clause) enables you to reuse the same
query block in a SELECT statement when it occurs more than once within a complex query.
This is particularly useful when a query has many references to the same query block and
there are joins and aggregations.
Using the WITH clause, you can reuse the same query when it is costly to evaluate the query
block and it occurs more than once within a complex query. Using the WITH clause, the
Oracle Server retrieves the results of a query block and stores it in the user’s temporary
tablespace. This can improve performance.
WITH Clause Benefits
• Makes the query easy to read
• Evaluates a clause only once, even if it appears multiple times in the query
• In most cases, may improve performance for large queries
WITH Clause
• Using the WITH clause, you can use the same query block
in a SELECT statement when it occurs more than once
within a complex query.
• The WITH clause retrieves the results of a query block and
stores it in the user’s temporary tablespace.
• The WITH clause may improve performance.

The problem in the slide would require the following intermediate calculations:
1. Calculate the total salary for every department, and store the result using a WITH
clause.
2. Calculate the average salary across departments, and store the result using a WITH
clause.
3. Compare the total salary calculated in the first step with the average salary calculated in
the second step. If the total salary for a particular department is greater than the average
salary across departments, display the department name and the total salary for that
department.
The solution for this problem is provided on the next page.
WITH Clause: Example
Using the WITH clause, write a query to display the department
name and total salaries for those departments whose total
salary is greater than the average salary across departments.

The SQL code in the slide is an example of a situation in which you can improve performance
and write SQL more simply by using the WITH clause. The query creates the query names
DEPT_COSTS and AVG_COST and then uses them in the body of the main query. Internally,
the WITH clause is resolved either as an inline view or a temporary table. The optimizer
chooses the appropriate resolution depending on the cost or benefit of temporarily storing the
results of the WITH clause.
The output generated by the SQL code in the slide is as follows:
WITH Clause Usage Notes
• It is used only with SELECT statements.
• A query name is visible to all WITH element query blocks (including their subquery
blocks) defined after it and the main query block itself (including its subquery blocks).
• When the query name is the same as an existing table name, the parser searches from
the inside out, and the query block name takes precedence over the table name.
• The WITH clause can hold more than one query. Each query is then separated by a
comma.
WITH Clause: Example
WITH
dept_costs AS (
SELECT d.department_name, SUM(e.salary) AS dept_total
FROM employees e JOIN departments d
ON e.department_id = d.department_id
GROUP BY d.department_name),
avg_cost AS (
SELECT SUM(dept_total)/COUNT(*) AS dept_avg
FROM dept_costs)
SELECT *
FROM dept_costs
WHERE dept_total >
(SELECT dept_avg
FROM avg_cost)
ORDER BY department_name;

The WITH clause has been extended to enable formulation of recursive queries.
Recursive WITH defines a recursive query with a name, the Recursive WITH element name.
The Recursive WITH element definition must contain at least two query blocks: an anchor
member and a recursive member. There can be multiple anchor members, but there can be
only a single recursive member.
Recursive WITH clause complies with the American National Standards Institute (ANSI)
standard.
Recursive WITH can be used to query hierarchical data such as organization charts.
Recursive WITH Clause
The Recursive WITH clause:
• Enables formulation of recursive queries
• Creates a query with a name, called the Recursive WITH
element name
• Contains two types of query block members: an anchor
and a recursive
• Is ANSI-compatible

Example 1 in the slide displays records from a FLIGHTS table describing flights between two
cities.
Using the query in example 2, you query the FLIGHTS table to display the total flight time
between any source and destination. The WITH clause in the query, which is named
Reachable From, has a UNION ALL query with two branches. The first branch is the anchor
branch, which selects all the rows from the Flights table. The second branch is the
recursive branch. It joins the contents of Reachable From to the Flights table to find
other cities that can be reached, and adds these to the content of Reachable From. The
operation will finish when no more rows are found by the recursive branch.
Example 3 displays the result of the query that selects everything from the WITH clause
element Reachable From.
For details, see:
• Oracle Database SQL Language Reference 12c Release 1.0
• Oracle Database Data Warehousing Guide 12c Release 1.0
Recursive WITH Clause: Example
WITH Reachable_From (Source, Destin, TotalFlightTime) AS
(
SELECT Source, Destin, Flight_time
FROM Flights
UNION ALL
SELECT incoming.Source, outgoing.Destin,
incoming.TotalFlightTime+outgoing.Flight_time
FROM Reachable_From incoming, Flights outgoing
WHERE incoming.Destin = outgoing.Source
)
SELECT Source, Destin, TotalFlightTime
FROM Reachable_From;
FLIGHTS Table 1
2
3

Answer: b
Quiz
With a correlated subquery, the inner SELECT statement drives
the outer SELECT statement.
a. True
b. False

You can use multiple-column subqueries to combine multiple WHERE conditions in a single
WHERE clause. Column comparisons in a multiple-column subquery can be pairwise
comparisons or nonpairwise comparisons.
You can use a subquery to define a table to be operated on by a containing query.
Scalar subqueries can be used in:
• The condition and expression part of DECODE and CASE
• All clauses of SELECT except GROUP BY
• A SET clause and WHERE clause of the UPDATE statement
from a table referred to in the parent statement. A correlated subquery is evaluated once for
each row processed by the parent statement. The parent statement can be a SELECT
statement. Using the WITH clause, you can reuse the same query when it is costly to re-
evaluate the query block and it occurs more than once within a complex query.
Summary
• Write a multiple-column subquery
• Use scalar subqueries in SQL
• Solve problems with correlated subqueries
• Update and delete rows by using correlated subqueries
• Use the EXISTS and NOT EXISTS operators
• Use the WITH clause

In this practice, you write multiple-column subqueries, and correlated and scalar subqueries.
You also solve problems by writing the WITH clause.
• Creating multiple-column subqueries
• Writing correlated subqueries
• Using the EXISTS operator
• Using scalar subqueries

Manipulating Data by Using Subqueries

In this lesson, you learn how to manipulate data in the Oracle database by using subqueries.
You also learn how to solve problems by using correlated subqueries.
Objectives
• Use subqueries to manipulate data
• Insert by using a subquery as a target
• Use the WITH CHECK OPTION keyword on DML
statements
• Use correlated subqueries to update and delete rows

Lesson Agenda
• Using subqueries to manipulate data
• Inserting by using a subquery as a target
• Using the WITH CHECK OPTION keyword on DML
statements
• Using correlated subqueries to update and delete rows

Subqueries can be used to retrieve data from a table that you can use as input to an INSERT
into a different table. In this way, you can easily copy large volumes of data from one table to
another with one single SELECT statement. Similarly, you can use subqueries to do mass
updates and deletes by using them in the WHERE clause of the UPDATE and DELETE
statements. You can also use subqueries in the FROM clause of a SELECT statement. This is
called an inline view.
Note: You learned how to update and delete rows based on another table in the course titled
Oracle Database: SQL Workshop I.
Using Subqueries to Manipulate Data
You can use subqueries in data manipulation language (DML)
statements to:
• Retrieve data by using an inline view
• Copy data from one table to another
• Update data in one table based on the values of another
table
• Delete rows from one table based on rows in another table

Lesson Agenda
statements

You can use a subquery in place of the table name in the INTO clause of the INSERT
statement. The SELECT list of this subquery must have the same number of columns as the
column list of the VALUES clause. Any rules on the columns of the base table must be
followed in order for the INSERT statement to work successfully. For example, you cannot put
in a duplicate location ID or leave out a value for a mandatory NOT NULL column.
This use of subqueries helps you avoid having to create a view just for performing an
INSERT.
The example in the slide uses a subquery in the place of LOC to create a record for a new
European city.
Note: You can also perform the INSERT operation on the EUROPEAN_CITIES view by using
the following code:
INSERT INTO european_cities
VALUES (3300,'Cardiff','UK');
For the example in the slide, the loc table is created by running the following statement:
CREATE TABLE loc AS SELECT * FROM locations;
Inserting by Using a Subquery as a Target
INSERT INTO (SELECT l.location_id, l.city, l.country_id
FROM loc l
JOIN countries c
WHERE region_name = 'Europe')
VALUES (3300, 'Cardiff', 'UK');

The example in the slide shows that the insert via the inline view created a new record in the
base table LOC.
The following example shows the results of the subquery that was used to identify the table
for the INSERT statement.
SELECT l.location_id, l.city, l.country_id
FROM loc l
JOIN countries c
WHERE region_name = 'Europe';
Inserting by Using a Subquery as a Target
Verify the results.
SELECT location_id, city, country_id
FROM loc;

Lesson Agenda
statements

Specify the WITH CHECK OPTION keyword to indicate that if the subquery is used in place of a
table in an INSERT, UPDATE, or DELETE statement, no changes that will produce rows that
are not included in the subquery are permitted to that table.
The example in the slide shows how to use an inline view with WITH CHECK OPTION. The
INSERT statement prevents the creation of records in the LOC table for a city that is not in
Europe.
The following example executes successfully because of the changes in the VALUES list.
INSERT INTO (SELECT location_id, city, country_id
FROM loc
WHERE country_id IN
(SELECT country_id
FROM countries
NATURAL JOIN regions
WITH CHECK OPTION)
VALUES (3500, 'Berlin', 'DE');
Using the WITH CHECK OPTION Keyword
on DML Statements
The WITH CHECK OPTION keyword prohibits you from changing
rows that are not in the subquery.
INSERT INTO ( SELECT location_id, city, country_id
FROM loc
WHERE country_id IN
(SELECT country_id
FROM countries
WITH CHECK OPTION )
VALUES (3600, 'Washington', 'US');
Error report:
SQL Error: ORA-01402: view WITH CHECK OPTION where-clause violation
01402. 00000 - "view WITH CHECK OPTION where-clause violation"
*Cause:
*Action:

The use of an inline view with the WITH CHECK OPTION provides an easy method to prevent
changes to the table.
To prevent the creation of a non-European city, you can also use a database view by
performing the following steps:
1. Create a database view:
CREATE OR REPLACE VIEW european_cities
AS
SELECT location_id, city, country_id
FROM locations
WHERE country_id in
(SELECT country_id
FROM countries
WITH CHECK OPTION;
2. Verify the results by inserting data:
INSERT INTO european_cities
VALUES (3400,'New York','US');
The second step produces the same error as shown in the slide.

Lesson Agenda
statements
Lesson AgendaLesson Agenda

In the case of the UPDATE statement, you can use a correlated subquery to update rows in
one table based on rows from another table.
Correlated UPDATE
Use a correlated subquery to update rows in one table based
on rows from another table.
UPDATE table1 alias1
SET column = (SELECT expression
FROM table2 alias2
WHERE alias1.column =
alias2.column);

The example in the slide denormalizes the EMPL6 table by adding a column to store the
department name and then populates the table by using a correlated update.
Following is another example for a correlated update.
Problem Statement
The REWARDS table has a list of employees who have exceeded expectations in their
performance. Use a correlated subquery to update rows in the EMPL6 table based on rows
from the REWARDS table:
UPDATE empl6
SET salary = (SELECT empl6.salary + rewards.pay_raise
FROM rewards
WHERE employee_id =
empl6.employee_id
AND payraise_date =
(SELECT MAX(payraise_date)
FROM rewards
WHERE employee_id = empl6.employee_id))
WHERE empl6.employee_id
IN (SELECT employee_id FROM rewards);
Using Correlated UPDATE
• Denormalize the EMPL6 table by adding a column to store
the department name.
• Populate the table by using a correlated update.
Using Correlated UPDATE
ALTER TABLE empl6
ADD(department_name VARCHAR2(25));
UPDATE empl6 e
SET department_name =
(SELECT department_name
FROM departments d
WHERE e.department_id = d.department_id);

This example uses the REWARDS table. The REWARDS table has the following columns:
EMPLOYEE_ID, PAY_RAISE, and PAYRAISE_DATE. Every time an employee gets a pay
raise, a record with details such as the employee ID, the amount of the pay raise, and the
date of receipt of the pay raise is inserted into the REWARDS table. The REWARDS table can
contain more than one record for an employee. The PAYRAISE _DATE column is used to
identify the most recent pay raise received by an employee.
In the example, the SALARY column in the EMPL6 table is updated to reflect the latest pay
raise received by the employee. This is done by adding the current salary of the employee
with the corresponding pay raise from the REWARDS table.

In the case of a DELETE statement, you can use a correlated subquery to delete only those
rows that also exist in another table. If you decide that you will maintain only the last four job
history records in the JOB_HISTORY table, when an employee transfers to a fifth job, you
delete the oldest JOB_HISTORY row by looking up the JOB_HISTORY table for the
MIN(START_DATE) for the employee. The following code illustrates how the preceding
operation can be performed using a correlated DELETE:
DELETE FROM job_history JH
WHERE employee_id =
(SELECT employee_id
FROM employees E
WHERE JH.employee_id = E.employee_id
AND START_DATE =
(SELECT MIN(start_date)
FROM job_history JH
WHERE JH.employee_id = E.employee_id)
AND 5 > (SELECT COUNT(*)
FROM job_history JH
WHERE JH.employee_id = E.employee_id
GROUP BY EMPLOYEE_ID
HAVING COUNT(*) >= 4));
DELETE FROM table1 alias1
WHERE column operator
(SELECT expression
FROM table2 alias2
WHERE alias1.column = alias2.column);
Correlated DELETE
Use a correlated subquery to delete rows in one table based on
rows from another table.

Example
Two tables are used in this example. They are:
• The EMPL6 table, which provides details of all the current employees
• The EMP_HISTORY table, which provides details of previous employees
EMP_HISTORY contains data regarding previous employees, so it would be erroneous if the
same employee’s record existed in both the EMPL6 and EMP_HISTORY tables. You can
delete such erroneous records by using the correlated subquery shown in the slide.
Using Correlated DELETE
Use a correlated subquery to delete only those rows from the
EMPL6 table that also exist in the EMP_HISTORY table.
DELETE FROM empl6 E
WHERE employee_id =
(SELECT employee_id
FROM emp_history
WHERE employee_id = E.employee_id);

In this lesson, you should have learned how to manipulate data in the Oracle database by
using subqueries. You learn how to use the WITH CHECK OPTION keyword on DML
statements and use correlated subqueries with UPDATE and DELETE statements.
Summary
• Manipulate data by using subqueries
• Insert by using a subquery as a target
• Use the WITH CHECK OPTION keyword on DML
statements
• Use correlated subqueries with UPDATE and DELETE
statements

In this practice, you learn the concepts of manipulating data by using subqueries, WITH
CHECK OPTION, and correlated subqueries to UPDATE and DELETE rows.
statements

Controlling User Access

In this lesson, you learn how to control database access to specific objects and add new
users with different levels of access privileges.
Objectives
After completing this lesson, you should be able to do the
following:
• Differentiate system privileges from object privileges
• Grant privileges on tables
• Grant roles
• Distinguish between privileges and roles

Lesson Agenda
• System privileges
• Creating a role
• Object privileges
• Revoking object privileges

In a multiple-user environment, you want to maintain security of database access and use.
With Oracle Server database security, you can do the following:
• Control database access.
• Give access to specific objects in the database.
• Confirm given and received privileges with the Oracle data dictionary.
Database security can be classified into two categories: system security and data security.
System security covers access and use of the database at the system level, such as the
username and password, the disk space allocated to users, and the system operations that
users can perform. Database security covers access and use of the database objects and the
actions that those users can perform on the objects.
Controlling User Access
Database
administrator
Users
Username and password
Privileges

A privilege is the right to execute particular SQL statements. The database administrator
(DBA) is a high-level user with the ability to create users and grant users access to the
database and its objects. Users require system privileges to gain access to the database and
object privileges to manipulate the content of the objects in the database. Users can also be
given the privilege to grant additional privileges to other users or to roles, which are named
groups of related privileges.
Schemas
A schema is a collection of objects such as tables, views, and sequences. The schema is
owned by a database user and has the same name as that user.
A system privilege is the right to perform a particular action, or to perform an action on any
schema objects of a particular type. An object privilege provides the user the ability to perform
a particular action on a specific schema object.
For more information, see the Oracle Database 2 Day DBA reference manual for Oracle
Database12c.
Privileges
• Database security:
– System security
– Data security
• System privileges: Performing a particular action within the
database
• Object privileges: Manipulating the content of the database
objects
• Schemas: Collection of objects such as tables, views, and
sequences

More than 200 distinct system privileges are available for users and roles. Typically, system
privileges are provided by the database administrator (DBA).
The table SYSTEM_PRIVILEGE_MAP contains all the system privileges available, based on
the version release. This table is also used to map privilege type numbers to type names.
Typical DBA Privileges
System Privilege Operations Authorized
CREATE USER Grantee can create other Oracle users.
DROP USER Grantee can drop another user.
DROP ANY TABLE Grantee can drop a table in any schema.
BACKUP ANY TABLE Grantee can back up any table in any schema with
the export utility.
SELECT ANY TABLE Grantee can query tables, views, or materialized
views in any schema.
CREATE ANY TABLE Grantee can create tables in any schema.
System Privileges
• More than 200 privileges are available.
• The database administrator has high-level system
privileges for tasks such as:
– Creating new users
– Removing users
– Removing tables
– Backing up tables

The DBA creates the user by executing the CREATE USER statement. The user does not have
any privileges at this point. The DBA can then grant privileges to that user. These privileges
determine what the user can do at the database level.
The slide gives the abridged syntax for creating a user.
In the syntax:
user Is the name of the user to be created
Password Specifies that the user must log in with this password
For more information, see the Oracle Database SQL Language Reference for Oracle
Database12c.
Note: Starting with Oracle Database 11g, passwords are case-sensitive.
Creating Users
The DBA creates users with the CREATE USER statement.
CREATE USER demo
IDENTIFIED BY demo;
CREATE USER user
IDENTIFIED BY password;

Typical User Privileges
After the DBA creates a user, the DBA can assign privileges to that user.
System Privilege Operations Authorized
CREATE SESSION Connect to the database.
CREATE TABLE Create tables in the user’s schema.
CREATE SEQUENCE Create a sequence in the user’s schema.
CREATE VIEW Create a view in the user’s schema.
CREATE PROCEDURE Create a stored procedure, function, or package in the user’s
schema.
User System Privileges
• After a user is created, the DBA can grant specific system
privileges to that user.
• An application developer, for example, may have the
following system privileges:
– CREATE SESSION
– CREATE TABLE
– CREATE SEQUENCE
– CREATE VIEW
– CREATE PROCEDURE
GRANT privilege [, privilege...]
TO user [, user| role, PUBLIC...];

In the syntax:
privilege Is the system privilege to be granted
user |role|PUBLIC Is the name of the user, the name of the role, or PUBLIC
(which designates that every user is granted the privilege)
Note: Current system privileges can be found in the SESSION_PRIVS dictionary view. Data
dictionary is a collection of tables and views created and maintained by the Oracle Server.
They contain information about the database.

The DBA uses the GRANT statement to allocate system privileges to the user. After the user
has been granted the privileges, the user can immediately use those privileges.
In the example in the slide, the demo user has been assigned the privileges to create
sessions, tables, sequences, and views.
Granting System Privileges
The DBA can grant specific system privileges to a user.
GRANT create session, create table,
create sequence, create view
TO demo;

Lesson Agenda
• Creating a role

A role is a named group of related privileges that can be granted to the user. This method
makes it easier to revoke and maintain privileges.
A user can have access to several roles, and several users can be assigned the same role.
Roles are typically created for a database application.
Creating and Assigning a Role
First, the DBA must create the role. Then the DBA can assign privileges to the role and assign
the role to users.
Syntax
CREATE ROLE role;
In the syntax:
role Is the name of the role to be created
After the role is created, the DBA can use the GRANT statement to assign the role to users as
well as assign privileges to the role. A role is not a schema object; therefore, any user can
add privileges to a role.
What Is a Role?
Allocating privileges
without a role
Allocating privileges
with a role
Privileges
Users
Manager

Creating a Role
The example in the slide creates a manager role and then enables the manager to create
tables and views. It then grants user alice the role of a manager. Now alice can create
tables and views.
If users have multiple roles granted to them, they receive all the privileges associated with all
the roles.
Creating and Granting Privileges to a Role
• Create a role:
• Grant privileges to a role:
• Grant a role to users:
CREATE ROLE manager;
GRANT create table, create view
TO manager;
GRANT manager TO alice;

The DBA creates an account and initializes a password for every user. You can change your
password by using the ALTER USER statement.
The slide example shows that the demo user changes the password by using the ALTER
USER statement.
Syntax
ALTER USER user IDENTIFIED BY password;
In the syntax:
user Is the name of the user
password Specifies the new password
Although this statement can be used to change your password, there are many other options.
You must have the ALTER USER privilege to change any other option.
Database 12c.
Note: SQL*Plus has a PASSWORD command (PASSW) that can be used to change the
password of a user when the user is logged in. This command is not available in SQL
Developer.
Changing Your Password
• The DBA creates your user account and initializes your
password.
• You can change your password by using the ALTER USER
statement.
ALTER USER demo
IDENTIFIED BY employ;

Lesson Agenda
• Creating a role

An object privilege is a privilege or right to perform a particular action on a specific table, view,
sequence, or procedure. Each object has a particular set of grantable privileges. The table in
the slide lists the privileges for various objects. Note that the only privileges that apply to a
sequence are SELECT and ALTER. UPDATE, REFERENCES, and INSERT can be restricted by
specifying a subset of updatable columns.
A SELECT privilege can be restricted by creating a view with a subset of columns and granting
the SELECT privilege only on the view. A privilege granted on a synonym is converted to a
privilege on the base table referenced by the synonym.
Note: With the REFERENCES privilege, you can ensure that other users can create FOREIGN
KEY constraints that reference your table.
Object Privileges
Object
privilege Table View Sequence
ALTER
DELETE
INDEX
INSERT
REFERENCES
SELECT
UPDATE

Granting Object Privileges
Different object privileges are available for different types of schema objects. A user
automatically has all object privileges for schema objects contained in the user’s schema. A
user can grant any object privilege on any schema object that the user owns to any other user
or role. If the grant includes WITH GRANT OPTION, the grantee can further grant the object
privilege to other users; otherwise, the grantee can use the privilege but cannot grant it to
other users.
In the syntax:
object_priv Is an object privilege to be granted
ALL Specifies all object privileges
columns Specifies the column from a table or view on which
privileges are granted
ON object Is the object on which the privileges are granted
TO Identifies to whom the privilege is granted
PUBLIC Grants object privileges to all users
WITH GRANT OPTION Enables the grantee to grant the object privileges to other
users and roles
Note: In the syntax, schema is the same as the owner’s name.
Object Privileges
• Object privileges vary from object to object.
• An owner has all the privileges on the object.
• An owner can give specific privileges on that owner’s
object.
GRANT object_priv [(columns)]
ON object
TO {user|role|PUBLIC}
[WITH GRANT OPTION];

Guidelines
• To grant privileges on an object, the object must be in your own schema, or you must
have been granted the object privileges WITH GRANT OPTION.
• An object owner can grant any object privilege on the object to any other user or role of
the database.
• The owner of an object automatically acquires all object privileges on that object.
The first example in the slide grants the demo user the privilege to query your EMPLOYEES
table. The second example grants UPDATE privileges on specific columns in the
DEPARTMENTS table to demo and to the manager role.
For example, if your schema is oraxx, and the demo user now wants to use a SELECT
statement to obtain data from your EMPLOYEES table, the syntax he or she must use is:
SELECT * FROM oraxx.employees;
Alternatively, the demo user can create a synonym for the table and issue a SELECT
statement from the synonym:
CREATE SYNONYM emp FOR oraxx.employees;
SELECT * FROM emp;
Note: DBAs generally allocate system privileges; any user who owns an object can grant
object privileges.
Granting Object Privileges
• Grant query privileges on the EMPLOYEES table:
• Grant privileges to update specific columns to users and
roles:
GRANT select
ON employees
TO demo;
GRANT update (department_name, location_id)
ON departments
TO demo, manager;

WITH GRANT OPTION Keyword
A privilege that is granted with the WITH GRANT OPTION clause can be passed on to other
users and roles by the grantee. Object privileges granted with the WITH GRANT OPTION
clause are revoked when the grantor’s privilege is revoked.
The example in the slide gives the demo user access to your DEPARTMENTS table with the
privileges to query the table and add rows to the table. The example also shows that demo
can give others these privileges.
PUBLIC Keyword
An owner of a table can grant access to all users by using the PUBLIC keyword.
The second example allows all users on the system to query data from DEPARTMENTS table.
Passing On Your Privileges
• Give a user authority to pass along privileges:
• Allow all users on the system to query data from
DEPARTMENTS table:
GRANT select, insert
ON departments
TO demo
WITH GRANT OPTION;
GRANT select
ON departments
TO PUBLIC;

If you attempt to perform an unauthorized operation, such as deleting a row from a table for
which you do not have the DELETE privilege, the Oracle server does not permit the operation
to take place.
If you receive the Oracle server error message “Table or view does not exist,” you have done
either of the following:
• Named a table or view that does not exist
• Attempted to perform an operation on a table or view for which you do not have the
appropriate privilege
The data dictionary is organized in tables and views and contains information about the
database. You can access the data dictionary to view the privileges that you have. The table
in the slide describes various data dictionary views.
You learn about data dictionary views in the lesson titled “Introduction to Data Dictionary
Views.”
Note: The ALL_TAB_PRIVS_MADE dictionary view describes all the object grants made by
the user or made on the objects owned by the user.
Confirming Granted Privileges
Data Dictionary View Description
ROLE_SYS_PRIVS System privileges granted to roles
ROLE_TAB_PRIVS Table privileges granted to roles
USER_ROLE_PRIVS Roles accessible by the user
USER_SYS_PRIVS System privileges granted to the user
USER_TAB_PRIVS_MADE Object privileges granted on the user’s objects
USER_TAB_PRIVS_RECD Object privileges granted to the user
USER_COL_PRIVS_MADE Object privileges granted on the columns of the user’s
objects
USER_COL_PRIVS_RECD Object privileges granted to the user on specific
columns

Lesson Agenda
• Creating a role

You can remove privileges granted to other users by using the REVOKE statement. When you
use the REVOKE statement, the privileges that you specify are revoked from the users you
name and from any other users to whom those privileges were granted by the revoked user.
In the syntax:
CASCADE Is required to remove any referential integrity constraints made to
the CONSTRAINTS object by means of the REFERENCES privilege
Database12c.
Note: If a user leaves the company and you revoke his or her privileges, you must regrant
any privileges that this user granted to other users. If you drop the user account without
revoking privileges from it, the system privileges granted by this user to other users are not
affected by this action.
Revoking Object Privileges
• You use the REVOKE statement to revoke privileges
granted to other users.
• Privileges granted to others through the WITH GRANT
OPTION clause are also revoked.
REVOKE {privilege [, privilege...]|ALL}
ON object
FROM {user[, user...]|role|PUBLIC}
[CASCADE CONSTRAINTS];

The example in the slide revokes SELECT and INSERT privileges given to the demo user on
the DEPARTMENTS table.
Note: If a user is granted a privilege with the WITH GRANT OPTION clause, that user can also
grant the privilege with the WITH GRANT OPTION clause, so that a long chain of grantees is
possible, but no circular grants (granting to a grant ancestor) are permitted. If the owner
revokes a privilege from a user who granted the privilege to other users, the revoking
cascades to all the privileges granted.
For example, if user A grants a SELECT privilege on a table to user B including the WITH
GRANT OPTION clause, user B can grant to user C the SELECT privilege with the WITH GRANT
OPTION clause as well, and user C can then grant to user D the SELECT privilege. If user A
revokes privileges from user B, the privileges granted to users C and D are also revoked.
Revoking Object Privileges
Revoke the SELECT and INSERT privileges given to the demo
user on the DEPARTMENTS table.
REVOKE select, insert
ON departments
FROM demo;

Answer: a, c, d
Quiz
Which of the following statements are true?
a. After a user creates an object, the user can pass along any
of the available object privileges to other users by using
the GRANT statement.
b. A user can create roles by using the CREATE ROLE
statement to pass along a collection of system or object
privileges to other users.
c. Users can change their own passwords.
d. Users can view the privileges granted to them and those
that are granted on their objects.

DBAs establish initial database security for users by assigning privileges to the users.
• The DBA creates users who must have a password. The DBA is also responsible for
establishing the initial system privileges for a user.
• After the user has created an object, the user can pass along any of the available object
privileges to other users or to all users by using the GRANT statement.
• A DBA can create roles by using the CREATE ROLE statement to pass along a collection
of system or object privileges to multiple users. Roles make granting and revoking
privileges easier to maintain.
• Users can change their passwords by using the ALTER USER statement.
• You can remove privileges from users by using the REVOKE statement.
• With data dictionary views, users can view the privileges granted to them and those that
are granted on their objects.
Summary
• Differentiate system privileges from object privileges
• Grant privileges on tables
• Grant roles
• Distinguish between privileges and roles

In this practice, you learn how to grant other users privileges to your table and modifying
another user’s table through the privileges granted to you.
• Granting other users privileges to your table
• Modifying another user’s table through the privileges
granted to you

Manipulating Data

In this lesson, you learn how to use the DEFAULT keyword in INSERT and UPDATE
statements to identify a default column value. You also learn about multitable INSERT
statements, the MERGE statement, performing flashback operations, and tracking changes in
the database.
Objectives
• Specify explicit default values in the INSERT and UPDATE
statements
• Describe the features of multitable INSERTs
• Use the following types of multitable INSERTs:
– Unconditional INSERT
– Conditional INSERT ALL
– Conditional INSERT FIRST
– Pivoting INSERT
• Merge rows in a table
• Perform flashback operations
• Track the changes made to data over a period of time

Lesson Agenda
• Specifying explicit default values in the INSERT and
UPDATE statements
• Using the following types of multitable INSERTs:
– Pivoting INSERT
• Merging rows in a table
• Performing flashback operations
• Tracking the changes to data over a period of time

The DEFAULT keyword can be used in INSERT and UPDATE statements to identify a default
column value. If no default value exists, a null value is used.
The DEFAULT option saves you from having to hard code the default value in your programs
or query the dictionary to find it, as was done before this feature was introduced. Hard-coding
the default is a problem if the default changes, because the code consequently needs
changing. Accessing the dictionary is not usually done in an application; therefore, this is a
very important feature.
Explicit Default Feature: Overview
• Use the DEFAULT keyword as a column value where the
default column value is desired.
• This allows the user to control where and when the default
value should be applied to data.
• Explicit defaults can be used in INSERT and UPDATE
statements.

Specify DEFAULT to set the column to the value previously specified as the default value for
the column. If no default value for the corresponding column has been specified, the Oracle
server sets the column to null.
In the first example in the slide, the INSERT statement uses a default value for the
MANAGER_ID column. If there is no default value defined for the column, a null value is
inserted instead.
The second example uses the UPDATE statement to set the MANAGER_ID column to a default
value for department 10. If no default value is defined for the column, it changes the value to
null.
Note: When creating a table, you can specify a default value for a column. This is discussed
in SQL Workshop I.
Using Explicit Default Values
• DEFAULT with INSERT:
• DEFAULT with UPDATE:
INSERT INTO deptm3
(department_id, department_name, manager_id)
VALUES (300, 'Engineering', DEFAULT);
UPDATE deptm3
SET manager_id = DEFAULT

You can use the INSERT statement to add rows to a table where the values are derived from
existing tables. In place of the VALUES clause, you use a subquery.
Syntax
INSERT INTO table [ (column , column) ] subquery;
In the syntax:
table Is the table name
column Is the name of the column in the table to populate
subquery Is the subquery that returns rows into the table
The number of columns and their data types in the column list of the INSERT clause must
match the number of values and their data types in the subquery. To create a copy of the
rows of a table, use SELECT * in the subquery.
INSERT INTO EMPL3
SELECT *
FROM employees;
Note: You use the LOG ERRORS clause in your DML statement to enable the DML operation
to complete regardless of errors. Oracle writes the details of the error message to an error-
logging table that you have created. For more information, see the Oracle Database SQL
Copying Rows from Another Table
• Write your INSERT statement with a subquery.
• Do not use the VALUES clause.
• Match the number of columns in the INSERT clause with
that in the subquery.
INSERT INTO sales_reps(id, name, salary, commission_pct)
SELECT employee_id, last_name, salary, commission_pct
FROM employees
WHERE job_id LIKE '%REP%';

Lesson Agenda
UPDATE statements
– Pivoting INSERT

In a multitable INSERT statement, you insert computed rows derived from the rows returned
from the evaluation of a subquery into one or more tables.
Multitable INSERT statements are useful in a data warehouse scenario. You need to load
your data warehouse regularly so that it can serve its purpose of facilitating business analysis.
To do this, data from one or more operational systems must be extracted and copied into the
warehouse. The process of extracting data from the source system and bringing it into the
data warehouse is commonly called ETL, which stands for extraction, transformation, and
loading.
During extraction, the desired data must be identified and extracted from many different
sources, such as database systems and applications. After extraction, the data must be
physically transported to the target system or an intermediate system for further processing.
Depending on the chosen means of transportation, some transformations can be done during
this process. For example, a SQL statement that directly accesses a remote target through a
gateway can concatenate two columns as part of the SELECT statement.
After data is loaded into the Oracle database, data transformations can be executed using
SQL operations. A multitable INSERT statement is one of the techniques for implementing
SQL data transformations.
Multitable INSERT Statements: Overview
INSERT ALL
INTO target_a VALUES(…,…,…)
INTO target_b VALUES(…,…,…)
INTO target_c VALUES(…,…,…)
SELECT …
FROM sourcetab
WHERE …;
Target_a
Target_b
Target_c
Sourcetab
Subquery

Multitable INSERT statements offer the benefits of the INSERT ... SELECT statement when
multiple tables are involved as targets. Without multitable INSERT, you had to deal with n
independent INSERT ... SELECT statements, thus processing the same source data n times
and increasing the transformation workload n times.
As with the existing INSERT ... SELECT statement, the new statement can be parallelized
and used with the direct-load mechanism for faster performance.
Each record from any input stream, such as a nonrelational database table, can now be
converted into multiple records for a more relational database table environment. To
alternatively implement this functionality, you were required to write multiple INSERT
statements.
Multitable INSERT Statements: Overview
• Use the INSERT…SELECT statement to insert rows into
multiple tables as part of a single DML statement.
• Multitable INSERT statements are used in data
warehousing systems to transfer data from one or more
operational sources to a set of target tables.
• They provide significant performance improvement over:
– Single DML versus multiple INSERT…SELECT statements
– Single DML versus a procedure to perform multiple inserts
by using the IF...THEN syntax

You use different clauses to indicate the type of INSERT to be executed. The types of
multitable INSERT statements are:
• Unconditional INSERT: For each row returned by the subquery, a row is inserted into
each of the target tables.
• Conditional INSERT ALL: For each row returned by the subquery, a row is inserted into
each target table if the specified condition is met.
• Conditional INSERT FIRST: For each row returned by the subquery, a row is inserted
into the very first target table in which the condition is met.
• Pivoting INSERT: This is a special case of the unconditional INSERT ALL.
Types of Multitable INSERT Statements
The different types of multitable INSERT statements are:
• Unconditional INSERT
• Conditional INSERT ALL
• Conditional INSERT FIRST
• Pivoting INSERT

The slide displays the generic format for multitable INSERT statements.
Unconditional INSERT: ALL into_clause
Specify ALL followed by multiple insert_into_clauses to perform an unconditional
multitable INSERT. The Oracle Server executes each insert_into_clause once for each
row returned by the subquery.
Conditional INSERT: conditional_insert_clause
Specify the conditional_insert_clause to perform a conditional multitable INSERT.
The Oracle Server filters each insert_into_clause through the corresponding WHEN
condition, which determines whether that insert_into_clause is executed. A single
multitable INSERT statement can contain up to 127 WHEN clauses.
Conditional INSERT: ALL
If you specify ALL, the Oracle Server evaluates each WHEN clause regardless of the results of
the evaluation of any other WHEN clause. For each WHEN clause whose condition evaluates to
true, the Oracle Server executes the corresponding INTO clause list.
Multitable INSERT Statements
• Syntax for multitable INSERT:
• conditional_insert_clause:
INSERT [conditional_insert_clause]
[insert_into_clause values_clause] (subquery)
[ALL|FIRST]
[WHEN condition THEN] [insert_into_clause values_clause]
[ELSE] [insert_into_clause values_clause]

Conditional INSERT: FIRST
If you specify FIRST, the Oracle Server evaluates each WHEN clause in the order in which it
appears in the statement. If the first WHEN clause evaluates to true, the Oracle Server executes
the corresponding INTO clause and skips subsequent WHEN clauses for the given row.
Conditional INSERT: ELSE Clause
For a given row, if no WHEN clause evaluates to true:
• If you have specified an ELSE clause, the Oracle Server executes the INTO clause list
associated with the ELSE clause
• If you did not specify an ELSE clause, the Oracle Server takes no action for that row
Restrictions on Multitable INSERT Statements
• You can perform multitable INSERT statements only on tables, and not on views or
materialized views.
• You cannot perform a multitable INSERT on a remote table.
• You cannot specify a table collection expression when performing a multitable INSERT.
• In a multitable INSERT, all insert_into_clauses cannot combine to specify more than
999 target columns.

The example in the slide inserts rows into both the SAL_HISTORY and the MGR_HISTORY
tables.
The SELECT statement retrieves the details of employee ID, hire date, salary, and manager
ID of those employees whose employee ID is greater than 200 from the EMPLOYEES table.
The details of the employee ID, hire date, and salary are inserted into the SAL_HISTORY
table. The details of employee ID, manager ID, and salary are inserted into the
MGR_HISTORY table.
This INSERT statement is referred to as an unconditional INSERT because no further
restriction is applied to the rows that are retrieved by the SELECT statement. All the rows
retrieved by the SELECT statement are inserted into the two tables: SAL_HISTORY and
MGR_HISTORY. The VALUES clause in the INSERT statements specifies the columns from the
SELECT statement that must be inserted into each of the tables. Each row returned by the
SELECT statement results in two insertions: one for the SAL_HISTORY table and one for the
MGR_HISTORY table.
Unconditional INSERT ALL
• Select the EMPLOYEE_ID, HIRE_DATE, SALARY, and
MANAGER_ID values from the EMPLOYEES table for those
employees whose EMPLOYEE_ID is greater than 200.
• Insert these values into the SAL_HISTORY and
MGR_HISTORY tables by using a multitable INSERT.
INSERT ALL
INTO sal_history VALUES(EMPID,HIREDATE,SAL)
INTO mgr_history VALUES(EMPID,MGR,SAL)
SELECT employee_id EMPID, hire_date HIREDATE,
salary SAL, manager_id MGR
FROM employees
WHERE employee_id > 200;

A total of 12 rows were inserted:
SELECT COUNT(*) total_in_sal FROM sal_history;
SELECT COUNT(*) total_in_mgr FROM mgr_history;

For all employees in the employees tables, if the employee was hired before 2005, insert that
employee record into the employee history. If the employee earns a sales commission, insert
the record information into the EMP_SALES table. The SQL statement is shown on the next
page.
Conditional INSERT ALL: Example
EMP_HISTORY
EMP_SALES
Employees
Hired before
2005
With sales
commission

The example in the slide is similar to the example in the previous slide because it inserts rows
into both the EMP_HISTORY and the EMP_SALES tables. The SELECT statement retrieves
details such as employee ID, hire date, salary, and commission percentage for all employees
from the EMPLOYEES table. Details such as employee ID, hire date, and salary are inserted
into the EMP_HISTORY table. Details such as employee ID, commission percentage, and
salary are inserted into the EMP_SALES table.
This INSERT statement is referred to as a conditional INSERT ALL because a further
restriction is applied to the rows that are retrieved by the SELECT statement. From the rows
that are retrieved by the SELECT statement, only those rows in which the hire date was prior
to 2005 are inserted in the EMP_HISTORY table. Similarly, only those rows where the value of
commission percentage is not null are inserted in the EMP_SALES table.
SELECT count(*) FROM emp_history;
SELECT count(*) FROM emp_sales;
Conditional INSERT ALL
INSERT ALL
WHEN HIREDATE < '01-JAN-05' THEN
INTO emp_history VALUES(EMPID,HIREDATE,SAL)
WHEN COMM IS NOT NULL THEN
INTO emp_sales VALUES(EMPID,COMM,SAL)
SELECT employee_id EMPID, hire_date HIREDATE,
salary SAL, commission_pct COMM
FROM employees;

You can also optionally use the ELSE clause with the INSERT ALL statement.
Example:
INSERT ALL
WHEN job_id IN
(select job_id FROM jobs WHERE job_title LIKE '%Manager%') THEN
INTO managers2(last_name,job_id,SALARY)
VALUES (last_name,job_id,SALARY)
WHEN SALARY>10000 THEN
INTO richpeople(last_name,job_id,SALARY)
VALUES (last_name,job_id,SALARY)
ELSE
INTO poorpeople VALUES (last_name,job_id,SALARY)
SELECT * FROM employees;
Result:
116 rows inserted

For all employees in the EMPLOYEES table, insert the employee information into the first target
table that meets the condition. In the example, if an employee has a salary of 2,000, the
record is inserted into the SAL_LOW table only. The SQL statement is shown on the next
page.
Conditional INSERT FIRST: Example
SAL_LOW
SAL_MID
EMPLOYEES
Salary < 5,000
5000 <= Salary
<= 10,000
SAL_HIGH
Otherwise
Scenario: If an employee
salary is 2,000, the
record is inserted into the
SAL_LOW table only.

The SELECT statement retrieves details such as employee ID, last name, and salary for every
employee in the EMPLOYEES table. For each employee record, it is inserted into the very first
target table that meets the condition.
This INSERT statement is referred to as a conditional INSERT FIRST. The WHEN salary
< 5000 condition is evaluated first. If this first WHEN clause evaluates to true, the Oracle
Server executes the corresponding INTO clause and inserts the record into the SAL_LOW
table. It skips subsequent WHEN clauses for this row.
If the row does not satisfy the first WHEN condition (WHEN salary < 5000), the next
condition (WHEN salary between 5000 and 10000) is evaluated. If this condition
evaluates to true, the record is inserted into the SAL_MID table, and the last condition is
skipped.
If neither the first condition (WHEN salary < 5000) nor the second condition (WHEN
salary between 5000 and 10000) is evaluated to true, the Oracle Server executes the
corresponding INTO clause for the ELSE clause.
Conditional INSERT FIRST
INSERT FIRST
WHEN salary < 5000 THEN
INTO sal_low VALUES (employee_id, last_name, salary)
WHEN salary between 5000 and 10000 THEN
INTO sal_mid VALUES (employee_id, last_name, salary)
ELSE
INTO sal_high VALUES (employee_id, last_name, salary)
SELECT employee_id, last_name, salary
FROM employees;

A total of 107 rows were inserted:
SELECT count(*) low FROM sal_low;
SELECT count(*) mid FROM sal_mid;
SELECT count(*) high FROM sal_high;

Pivoting is an operation in which you must build a transformation such that each record from
any input stream, such as a nonrelational database table, must be converted into multiple
records for a more relational database table environment.
Suppose you receive a set of sales records from a nonrelational database table:
SALES_SOURCE_DATA, in the following format:
EMPLOYEE_ID, WEEK_ID, SALES_MON, SALES_TUE, SALES_WED,
SALES_THUR, SALES_FRI
You want to store these records in the SALES_INFO table in a more typical relational format:
EMPLOYEE_ID, WEEK, SALES
To solve this problem, you must build a transformation such that each record from the original
nonrelational database table, SALES_SOURCE_DATA, is converted into five records for the
data warehouse’s SALES_INFO table. This operation is commonly referred to as pivoting.
The solution to this problem is shown on the next page.
Pivoting INSERT
Convert the set of sales records from the nonrelational
database table to relational format.
600050004000300020006176
FRITHURWEDTUESMONWeek_IDEmp_ID
60006176
50006176
40006176
30006176
20006176
SALESWEEKEmployee_ID

In the example in the slide, the sales data is received from the nonrelational database table
SALES_SOURCE_DATA, which is the details of the sales performed by a sales representative
on each day of a week, for a week with a particular week ID.
DESC SALES_SOURCE_DATA
Pivoting INSERT
INSERT ALL
INTO sales_info VALUES (employee_id,week_id,sales_MON)
INTO sales_info VALUES (employee_id,week_id,sales_TUE)
INTO sales_info VALUES (employee_id,week_id,sales_WED)
INTO sales_info VALUES (employee_id,week_id,sales_THUR)
INTO sales_info VALUES (employee_id,week_id, sales_FRI)
SELECT EMPLOYEE_ID, week_id, sales_MON, sales_TUE,
sales_WED, sales_THUR,sales_FRI
FROM sales_source_data;

SELECT * FROM SALES_SOURCE_DATA;
DESC SALES_INFO
SELECT * FROM sales_info;
Observe in the preceding example that by using a pivoting INSERT, one row from the
SALES_SOURCE_DATA table is converted into five records for the relational table, SALES_INFO.

Lesson Agenda
UPDATE statements
– Pivoting INSERT

The Oracle Server supports the MERGE statement for INSERT, UPDATE, and DELETE
operations. Using this statement, you can update, insert, or delete a row conditionally into a
table, thus avoiding multiple DML statements. The decision whether to update, insert, or
delete into the target table is based on a condition in the ON clause.
You must have the INSERT and UPDATE object privileges on the target table and the SELECT
object privilege on the source table. To specify the DELETE clause of
merge_update_clause, you must also have the DELETE object privilege on the target
table.
The MERGE statement is deterministic. You cannot update the same row of the target table
multiple times in the same MERGE statement.
An alternative approach is to use PL/SQL loops and multiple DML statements. The MERGE
statement, however, is easy to use and more simply expressed as a single SQL statement.
The MERGE statement is suitable in a number of data warehousing applications. For example,
in a data warehousing application, you may need to work with data coming from multiple
sources, some of which may be duplicates. With the MERGE statement, you can conditionally
add or modify rows.
MERGE Statement
• Provides the ability to conditionally update, insert, or delete
data into a database table
• Performs an UPDATE if the row exists, and an INSERT if it
is a new row:
– Avoids separate updates
– Increases performance and ease of use
– Is useful in data warehousing applications

Merging Rows
You can update existing rows, and insert new rows conditionally by using the MERGE
statement. Using the MERGE statement, you can delete obsolete rows at the same time as you
update rows in a table. To do this, you include a DELETE clause with its own WHERE clause in
the syntax of the MERGE statement.
In the syntax:
INTO clause Specifies the target table you are updating or inserting into
USING clause Identifies the source of the data to be updated or inserted; can be
a table, view, or subquery
ON clause The condition on which the MERGE operation either updates or
inserts
WHEN MATCHED | Instructs the server how to respond to the results of the join
condition
WHEN NOT MATCHED
Note: For more information, see Oracle Database SQL Language Reference for Oracle
Database 12c.
MERGE Statement Syntax
You can conditionally insert, update, or delete rows in a table
by using the MERGE statement.
MERGE INTO table_name table_alias
USING (table|view|sub_query) alias
ON (join condition)
WHEN MATCHED THEN
UPDATE SET
col1 = col1_val,
col2 = col2_val
WHEN NOT MATCHED THEN
INSERT (column_list)
VALUES (column_values);

MERGE INTO copy_emp3 c
USING (SELECT * FROM EMPLOYEES ) e
ON (c.employee_id = e.employee_id)
WHEN MATCHED THEN
UPDATE SET
c.first_name = e.first_name,
c.last_name = e.last_name,
c.email = e.email,
c.phone_number = e.phone_number,
c.hire_date = e.hire_date,
c.job_id = e.job_id,
c.salary = e.salary*2,
c.commission_pct = e.commission_pct,
c.manager_id = e.manager_id,
c.department_id = e.department_id
DELETE WHERE (E.COMMISSION_PCT IS NOT NULL)
WHEN MATCHED THEN
UPDATE SET
...
INSERT VALUES(e.employee_id, e.first_name, e.last_name,
e.email, e.phone_number, e.hire_date, e.job_id,
e.salary, e.commission_pct, e.manager_id,
e.department_id);
Merging Rows: Example
Insert or update rows in the COPY_EMP3 table to match the
EMPLOYEES table.

INSERT VALUES(e.employee_id, e.first_name, e.last_name,
e.email, e.phone_number, e.hire_date, e.job_id,
e.salary, e.commission_pct, e.manager_id,
e.department_id);
The COPY_EMP3 table is created by using the following code:
CREATE TABLE COPY_EMP3 AS SELECT * FROM EMPLOYEES
WHERE SALARY<10000;
Then query the COPY_EMP3 table.
SELECT employee_id, salary, commission_pct FROM COPY_EMP3;
Observe that there are some employees with SALARY < 10000 and there are two employees
with COMMISSION_PCT.
The example in the slide matches the EMPLOYEE_ID in the COPY_EMP3 table to the
EMPLOYEE_ID in the EMPLOYEES table. If a match is found, the row in the COPY_EMP3 table is
updated to match the row in the EMPLOYEES table and the salary of the employee is doubled.
The records of the two employees with values in the COMMISSION_PCT column are deleted. If
the match is not found, rows are inserted into the COPY_EMP3 table.
...
...

The examples in the slide show that the COPY_EMP3 table is empty. The c.employee_id =
e.employee_id condition is evaluated. The condition returns false—there are no matches.
The logic falls into the WHEN NOT MATCHED clause, and the MERGE command inserts the rows
of the EMPLOYEES table into the COPY_EMP3 table. This means that the COPY_EMP3 table
now has exactly the same data as in the EMPLOYEES table.
SELECT employee_id, salary, commission_pct from copy_emp3;
…
Merging Rows: Example
WHEN MATCHED THEN
UPDATE SET
...
INSERT VALUES(e.employee_id, e.first_name, ...
TRUNCATE TABLE copy_emp3;
SELECT * FROM copy_emp3;
no rows selected
SELECT * FROM copy_emp3;
107 rows selected.

Lesson Agenda
UPDATE statements
– Pivoting INSERT

Oracle Flashback Table enables you to recover tables to a specified point in time with a single
statement. You can restore table data along with associated indexes and constraints while the
database is online, undoing changes to only the specified tables.
The Flashback Table feature is similar to a self-service repair tool. For example, if a user
accidentally deletes important rows from a table and then wants to recover the deleted rows,
you can use the FLASHBACK TABLE statement to restore the table to the time before the
deletion and see the missing rows in the table.
When using the FLASHBACK TABLE statement, you can revert the table and its contents to a
certain time or to an SCN.
Note: The SCN is an integer value associated with each change to the database. It is a
unique incremental number in the database. Every time you commit a transaction, a new SCN
is recorded.
FLASHBACK TABLE Statement
• Enables you to recover tables to a specified point in time
with a single statement
• Restores table data along with associated indexes and
constraints
• Enables you to revert the table and its contents to a certain
point in time or system change number (SCN)
SCN

Self-Service Repair Facility
Oracle Database provides a SQL data definition language (DDL) command, FLASHBACK
TABLE, to restore the state of a table to an earlier point in time in case it is inadvertently
deleted or modified. The FLASHBACK TABLE command is a self-service repair tool to restore
data in a table along with associated attributes such as indexes or views. This is done, while
the database is online, by rolling back only the subsequent changes to the given table.
Compared to traditional recovery mechanisms, this feature offers significant benefits such as
ease of use, availability, and faster restoration. It also takes the burden off the DBA to find and
restore application-specific properties. The flashback table feature does not address physical
corruption caused because of a bad disk.
Syntax
You can invoke a FLASHBACK TABLE operation on one or more tables, even on tables in
different schemas. You specify the point in time to which you want to revert by providing a
valid time stamp. By default, database triggers are disabled during the flashback operation for
all tables involved. You can override this default behavior by specifying the ENABLE
TRIGGERS clause.
Note: For more information about recycle bin and flashback semantics, refer to Oracle
Database Administrator’s Guide for Oracle Database 12c.
FLASHBACK TABLE Statement
• Repair tool for accidental table modifications
– Restores a table to an earlier point in time
– Offers ease of use, availability, and fast execution
– Is performed in place
• Syntax:
FLASHBACK TABLE [ schema. ] table [, [ schema.
] table ]... TO { { { SCN | TIMESTAMP } expr |
RESTORE POINT restore_point } [ { ENABLE |
DISABLE } TRIGGERS ] | BEFORE DROP [ RENAME TO
table ] } ;

Syntax and Examples
The example restores the EMP3 table to a state before a DROP statement.
The recycle bin is actually a data dictionary table containing information about dropped
objects. Dropped tables and any associated objects—such as, indexes, constraints, nested
tables, and so on—are not removed and still occupy space. They continue to count against
user space quotas until specifically purged from the recycle bin, or until they must be purged
by the database because of tablespace space constraints.
Each user can be thought of as an owner of a recycle bin because, unless a user has the
SYSDBA privilege, the only objects that the user has access to in the recycle bin are those that
the user owns. A user can view his or her objects in the recycle bin by using the following
statement:
SELECT * FROM RECYCLEBIN;
When you drop a user, any objects belonging to that user are not placed in the recycle bin
and any objects in the recycle bin are purged.
You can purge the recycle bin with the following statement:
PURGE RECYCLEBIN;
Using the FLASHBACK TABLE Statement
DROP TABLE emp3;
FLASHBACK TABLE emp3 TO BEFORE DROP;
…
SELECT original_name, operation, droptime FROM
recyclebin;

Lesson Agenda
UPDATE statements
– Pivoting INSERT

You may discover that, somehow, data in a table has been inappropriately changed. To
research this, you can use multiple flashback queries to view row data at specific points in
time. More efficiently, you can use the Flashback Version Query feature to view all changes to
a row over a period of time. This feature enables you to append a VERSIONS clause to a
SELECT statement that specifies a system change number (SCN) or the time stamp range
within which you want to view changes to row values. The query also can return associated
metadata, such as the transaction responsible for the change.
Further, after you identify an erroneous transaction, you can use the Flashback Transaction
Query feature to identify other changes that were done by the transaction. You then have the
option of using the Flashback Table feature to restore the table to a state before the changes
were made.
You can use a query on a table with a VERSIONS clause to produce all the versions of all the
rows that exist, or ever existed, between the time the query was issued and the
undo_retention seconds before the current time. undo_retention is an initialization
parameter, which is an autotuned parameter. A query that includes a VERSIONS clause is
referred to as a version query. The results of a version query behaves as though the WHERE
clause were applied to the versions of the rows. The version query returns versions of the
rows only across transactions.
System change number (SCN): The Oracle server assigns an SCN to identify the redo
records for each committed transaction.
Tracking Changes in Data
Versions of retrieved rows
SELECT
…
Version
query

In the example in the slide, the salary for employee 107 is retrieved (1). The salary for employee
107 is increased by 30 percent and this change is committed (2). The different versions of salary
are displayed (3).
The VERSIONS clause does not change the plan of the query. For example, if you run a query on
a table that uses the index access method, the same query on the same table with a VERSIONS
clause continues to use the index access method. The versions of the rows returned by the
version query are versions of the rows across transactions. The VERSIONS clause has no effect
on the transactional behavior of a query. This means that a query on a table with a VERSIONS
clause still inherits the query environment of the ongoing transaction.
The default VERSIONS clause can be specified as VERSIONS BETWEEN {SCN|TIMESTAMP}
MINVALUE AND MAXVALUE. The VERSIONS clause is a SQL extension only for queries. You
can have DML and DDL operations that use a VERSIONS clause within subqueries. The row
version query retrieves all the committed versions of the selected rows. Changes made by the
current active transaction are not returned. The version query retrieves all incarnations of the
rows. This essentially means that versions returned include deleted and subsequent reinserted
versions of the rows. The row access for a version query can be defined in one of the following
two categories:
• ROWID-based row access: In case of ROWID-based access, all versions of the specified
ROWID are returned irrespective of the row content. This essentially means that all versions
of the slot in the block indicated by the ROWID are returned.
• All other row access: For all other row access, all versions of the rows are returned.
Flashback Version Query: Example
SELECT salary FROM employees3
UPDATE employees3 SET salary = salary * 1.30
COMMIT;
SELECT salary FROM employees3
VERSIONS BETWEEN SCN MINVALUE AND MAXVALUE
1
2
3
1 3

You can use the VERSIONS BETWEEN clause to retrieve all the versions of the rows that exist
or have ever existed between the time the query was issued and a point back in time.
If the undo retention time is less than the lower bound time or the SCN of the BETWEEN
clause, the query retrieves versions up to the undo retention time only. The time interval of the
BETWEEN clause can be specified as an SCN interval or a wall-clock interval. This time
interval is closed at both the lower and the upper bounds.
In the example, Lorentz’s salary changes are retrieved. The NULL value for END_DATE for the
first version indicates that this was the existing version at the time of the query. The NULL
value for START_DATE for the last version indicates that this version was created at a time
before the undo retention time.
VERSIONS BETWEEN Clause
SELECT versions_starttime "START_DATE",
versions_endtime "END_DATE",
salary
FROM employees
VERSIONS BETWEEN SCN MINVALUE
AND MAXVALUE
WHERE last_name = 'Lorentz';

Answer: a
Quiz
When you use the INSERT or UPDATE command, the DEFAULT
keyword saves you from hard-coding the default value in your
programs or querying the dictionary to find it.
a. True
b. False

Answer: b
Quiz
In all the cases, when you execute a DROP TABLE command,
the database renames the table and places it in a recycle bin,
from where it can later be recovered by using the FLASHBACK
TABLE statement.
a. True
b. False

In this lesson, you also should have learned about multitable INSERT statements, the MERGE
statement, and tracking changes in the database.
Summary
• Specify explicit default values in the INSERT and UPDATE
statements
• Describe the features of multitable INSERTs
• Use the following types of multitable INSERTs:
– Pivoting INSERT
• Merge rows in a table
• Perform flashback operations

In this practice, you learn how to perform multitable INSERTS, MERGE operations, flashback
operations and tracking row versions.
• Performing multitable INSERTs
• Performing MERGE operations
• Tracking row versions

Oracle database 12c sql worshop 2 student guide vol 1

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