SQL Queries

Database Systems
Structure Query Language
(SQL)

Dr. Ejaz Ahmed 2
Objectives
• Example Tables
• Introduction
• ISO SQL Data Types
• Comparison Operators in SQL
• Logical Operators in SQL
• Arithmetic Operators in SQL
• SQL Schema and Catalog
• SQL Data Definition Statements (DDL)
• SQL Data Manipulation Statements (DML)
• Other SQL Operators

Dr. Ejaz Ahmed 3
Example Table …
Car_Sales
City Year Cars_sol
d
Dhahran 2001 525
Dhahran 2002 456
Riyadh 2001 700
Riyadh 2002 654
Jeddah 2001 921
Jeddah 2002 752
Khobar 2002

Dr. Ejaz Ahmed 4
Example: Tables …
1
2
3
ICS
COE
SWE
dno dname
Lid Lname dno salary
1
2
3
4
5
6
7
Ahmed
Amin
Hani
Abdallah
Ageel
Yousef
Khalid
1
2
1
1
2
2
4000
3700
4200
4300
4000
3500
4500
Departments
Lecturers

Dr. Ejaz Ahmed 5
Objectives of SQL
• Ideally, database language should allow user to:
– create the database and relation structures;
– perform insertion, modification, deletion of data from relations;
– perform simple and complex queries.
• Must perform these tasks with minimal user effort and command
structure and syntax must be easy to learn.
• It must be portable.
• SQL does not contain flow control commands. These must be
implemented using a programming or job-control language, or
interactively by the decisions of the user.

Dr. Ejaz Ahmed 6
Objectives of SQL …
• SQL is relatively easy to learn:
– It is a non-procedural language - you specify what information you
require, rather than how to get it.
– It is essentially free-format.
• Can be used by a range of users including DBAs, management,
application programmers, and other types of end users.
• An ISO standard now exists for SQL, making it both the formal and
de facto standard language for relational databases.

Dr. Ejaz Ahmed 7
Objectives of SQL …
• Consists of standard English words:
CREATE TABLE staff(
sno VARCHAR(5),
lname VARCHAR(15),
salary NUMBER(7,2)
);
INSERT INTO staff
VALUES ('SG16', 'Brown', 8300);
SELECT sno, lname, salary
FROM staff
WHERE salary > 10000;

Dr. Ejaz Ahmed 8
History of SQL …
• In 1974, D. Chamberlin (IBM San Jose Laboratory) defined
language called 'Structured English Query Language' or SEQUEL.
• A revised version SEQUEL/2 was defined in 1976 but name was
subsequently changed to SQL for legal reasons.
• Still pronounced 'see-quel', though official pronunciation is 's-q-l'.
• IBM subsequently produced a prototype DBMS called System R,
based on SEQUEL/2.
• Roots of SQL, however, are in SQUARE (Specifying Queries as
Relational Expressions), which predates System R project.

Dr. Ejaz Ahmed 9
History of SQL …
• In late 70s, ORACLE appeared and was probably first commercial
RDBMS based on SQL.
• In 1987, ANSI and ISO published an initial standard for SQL.
• In 1989, ISO published an addendum that defined an 'Integrity
Enhancement Feature'.
• In 1992, first major revision to ISO standard occurred, referred to as
SQL2 or SQL/92.

Dr. Ejaz Ahmed 10
Importance of SQL …
• SQL has become part of application architectures such
as IBM's Systems Application Architecture (SAA).
• It is strategic choice of many large and influential
organizations (e.g. X/OPEN).
• SQL is Federal Information Processing Standard (FIPS)
to which conformance is required for all sales of
databases to American Government.

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Importance of SQL …
• SQL Access Group trying to define enhancements that
will support interoperability across disparate systems.
• SQL is used in other standards and even influences
development of other standards as a definitional tool.
Examples include:
– ISO's Information Resource Directory System (IRDS)
Standard
– Remote Data Access (RDA) Standard.

Dr. Ejaz Ahmed 12
Components of SQL
• A database language must have support for the
components listed below. Most implementations of SQL
support various components listed below:
– Data Definition Language (DDL)
– Interactive Data Manipulation Language (Interactive
DML)
– Embedded Data Manipulation Language (Embedded
DML)
– Views
– Integrity and transaction control
– Authorization & Security (DCL)
– Catalog and dictionary facility.

Dr. Ejaz Ahmed 13
Basic Guidelines for Writing SQL
Statements …
• SQL statement consists of reserved words and user-defined words.
– Reserved words are a fixed part of SQL and must be spelt exactly as
required and cannot be split across lines.
– User-defined words are made up by user and represent names of
various database objects such as relations, columns, views.
• Most components of an SQL statement are case insensitive, except
for literal character data.
• More readable with indentation and lineation:
– Each clause should begin on a new line.
– Start of a clause should line up with start of other clauses.
– If clause has several parts, should each appear on a separate line and
be indented under start of clause.

Dr. Ejaz Ahmed 14
Basic Guidelines for Writing SQL
Statements …
• Use extended form of BNF notation:
– Upper case letters represent reserved words.
– Lower case letters represent user-defined words.
– | indicates a choice among alternatives.
– Curly braces indicate a required element.
– Square brackets indicate an optional element.
– … indicates optional repetition (0 or more).
– ALL SQL is case less

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ISO SQL Data Types

Dr. Ejaz Ahmed 16
Comparison Operators in SQL
• There are six comparison operators in SQL. These operators are
used to build conditions that are used in the WHERE clause of a
DML statement:
Operator Meaning
=
<>
<
>
<=
>=
Equal
Not Equal
Less than
Greater than
Less than or Eqaul
Greater than or Eqaul

Dr. Ejaz Ahmed 17
Logical Operators in SQL
• There are three logical operators that help us to build
compound conditions to be used in the WHERE clause
of the SELECT statement.
– The AND operator joins two or more conditions, and
display a row only if that row’s data satisfies ALL the
specified conditions.
– The OR operator joins two or more conditions, and
display a row only if that row’s data satisfies any of
the specified conditions.
– The NOT is a unary operator, and is used to negates
a condition.

Dr. Ejaz Ahmed 18
Arithmetic Operators in SQL
• Another feature of SQL allows the use of arithmetic in
queries.
– The standard arithmetic operators ( +, -, /, *) can be
applied to numeric values or attributes with numeric
domain.
– The arithmetic operators can be used in expressions
in the SELECT and the WHERE clauses to compute
numeric values.
– All attributes that can be computed using arithmetic
expressions (such as age from birth date, annual
salary from monthly salary) must be eliminated as
part of a good design practice in databases.

Dr. Ejaz Ahmed 19
SQL Schema and Catalog
• In SQL92, relations and other database objects exist in an
environment.
• Each environment contains one or more catalogs, and each catalog
consists of set of schemas.
• Schema is a named collection of related database objects.
• Objects in a schema can be tables, views, domains, constraints,
translations, and character sets. All have same owner.

Dr. Ejaz Ahmed 20
SELECT
• SELECT Definition
• Selecting Columns
• Selecting Rows
• Sorting
• Aggregation
• Grouping
• Restricting Groups
• Aliasing Table Names
• Nested Queries
• Join
• Set Operations

Dr. Ejaz Ahmed 21
SELECT Definition …
• SQL has only one statement for retrieving information from a
database called the SELECT statement.
• SQL SELECT statement is different from that of Relational Algebra.
• An important distinction between SQL and formal relational model
is that SQL allows duplicate rows. Hence an SQL table is not a set
but a multiset (some times called a bag) of tuples.

Retrieving Information From the
Database
DB
Data
JohnSmith
Mary
Stiles
22Dr. Ejaz Ahmed

Dr. Ejaz Ahmed 25
• A SELECT statement can consist up to six clauses.
SELECT [DISTINCT | ALL]
{* | [column_expression [AS
new_name]] [,...] }
FROM table_name [alias] [, ...]
[WHERE condition]
[GROUP BY column_list]
[HAVING condition]
[ORDER By column_list]
• Only SELECT and FROM clauses are mandatory.
• Order of the clauses cannot be changed.

Dr. Ejaz Ahmed 26
• FROM Specifies table(s) to be used.
• WHERE Filters rows.
• GROUP BY Forms groups of rows with same column value.
• HAVING Filters groups subject to some condition.
• SELECT Specifies which columns are to appear in output.
• ORDER BY Specifies the order of the output.

Dr. Ejaz Ahmed 27
Selecting Columns
• Selecting all columns +
• Selecting Specific columns +
• Selecting Computed columns +
• Renaming Columns +

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Selecting All Columns
Example 1:
SELECT city, year, cars_sold
FROM car_sales;
• Can use * as an abbreviation
for 'all columns':
Example 2:
SELECT *
FROM car_sales;
City Year Cars_sol
d
Dhahran 2001 525
Dhahran 2002 456
Riyadh 2001 700
Riyadh 2002 654
Jeddah 2001 921
Jeddah 2002 752
Khobar 2002
Input Tables

Dr. Ejaz Ahmed 29
Selecting Specific Columns
• Selected columns can be listed
as shown in the following
example. Notice that the year
column was not selected so it
doesn’t appear in the output.
Example:
SELECT city, cars_sold
FROM car_sales;
City Cars_sold
Dhahran 525
Dhahran 456
Riyadh 700
Riyadh 654
Jeddah 921
Jeddah 752
Khobar
Input Tables

Dr. Ejaz Ahmed 30
Selecting Computed Columns
• If the value of a car
is 100,000 then the
total sales per year
for each city is
computed as follows.
Example:
SELECT
city
,year
,cars_sold
,cars_sold * 100000
FROM car_sales;
Dhahran
Dhahran
Riyadh
Riyadh
Jeddah
Jeddah
2001
2002
2001
2002
2001
2002
525
456
700
654
921
752
City Year Cars_Sold
52500000
45600000
70000000
65400000
92100000
75200000
Cars_Sold *100000
Khobar 2002 00
Input Tables

Dr. Ejaz Ahmed 31
Renaming Columns
• The name of the
computed column in
the last slide cab be
changed from
cars_sold*100000 to
sales as follows.
Example:
SELECT
city
,year
,cars_sold As Sold
,cars_sold * 100000
AS sales
FROM car_sales;
Dhahran
Dhahran
Riyadh
Riyadh
Jeddah
Jeddah
2001
2002
2001
2002
2001
2002
525
456
700
654
921
752
City Year Sold
52500000
45600000
70000000
65400000
92100000
75200000
sales
Khobar 2002 00
Input Tables

Dr. Ejaz Ahmed 32
Selecting Rows
• Selecting All Rows +
• Partial match Search +
• Range Search +
• Set Membership Search +
• Pattern matching Search +
• Null Search +
• Removing Duplicate Rows +

Dr. Ejaz Ahmed 33
Selecting All Rows
• A SELECT statement without a
WHERE clause selects all
rows.
Example:
SELECT *
FROM car_sales;
Dhahran
Dhahran
Riyadh
Riyadh
Jeddah
Jeddah
2001
2002
2001
2002
2001
2002
525
456
700
654
921
752
City Year Cars_Sold
Khobar 2002
Input Tables

Dr. Ejaz Ahmed 34
Selecting Rows
• To Select certain rows of a table you need to use the
WHERE clause of the SELECT statement.
• The WHERE clause has a condition which is a logical
expression.
• The Where condition consists of:
– Comparison Operators
– Logical Operators
– Arithmetic Operators
– Other SQL constructs which will be discussed later.
• A record to be selected it must make the WHERE logical
expression true. In other words it must satisfy the where
condition.

Dr. Ejaz Ahmed 35
Partial match Search
• Selecting all the records whose column
values match the column values
specified in the WHERE clause.
Example1:
SELECT *
FROM car_sales
WHERE city = ‘Dhahran’;
Dhahran
Dhahran
2001
2002
525
456
City Year Cars_Sold
Dhahran 2002 456
City Year Cars_Sold
Example2:
SELECT *
FROM car_sales
WHERE city = ‘Dhahran’
AND year > 2001;
Input Tables

Dr. Ejaz Ahmed 36
Range Search
Example:
SELECT *
FROM car_sales
WHERE cars_sold >= 525
AND cars_sold <= 752;
OR
SELECT *
FROM car_sales
WHERE cars_sold
BETWEEN 525 AND 752;
Dhahran
Riyadh
Riyadh
Jeddah
2001
2001
2002
2002
525
700
654
752
City Year Sold
Selecting all the records whose column values is between the
values specified in the WHERE cluause.
 BETWEEN test includes the endpoints of range. NOT BETWEEN list the one not in the range.
Input Tables

Dr. Ejaz Ahmed 37
Set Membership Search …
Example:
SELECT *
FROM car_sales
WHERE city
IN
(‘Dhahran’, ‘Riyadh’);
Selecting all the records whose column value is a member of the
set specified in the WHERE clause.
Dhahran
Dhahran
Riyadh
Riyadh
2001
2002
2001
2002
525
456
700
654
City Year Sold
Input Tables

Dr. Ejaz Ahmed 38
Set Membership Search
Example:
SELECT *
FROM car_sales
WHERE city
NOT IN
(‘Dhahran’, ‘Riyadh’);
Selecting all the records whose column value not a member of the
set specified in the WHERE clause.
Jeddah
Jeddah
2001
2002
921
752
City Year Sold
Khobar 2002
Input Tables

Dr. Ejaz Ahmed 39
Pattern Matching Search …
• SQL has two special pattern matching
symbols:
– %: sequence of zero or more characters;
– _ (underscore): any single character.
• LIKE '%dd%' means a sequence of
characters of any length containing ‘dd'.

Dr. Ejaz Ahmed 40
Pattern matching Search
Example:
SELECT *
FROM car_sales
WHERE
city LIKE ‘J%’
Selecting all the records whose column value match the pattern specified in
the WHERE clause.
Jeddah
Jeddah
2001
2002
921
752
City Year Sold
Example:
SELECT *
FROM car_sales
WHERE
city LIKE ‘%dd%’
Jeddah
Jeddah
2001
2002
921
752
City Year Sold
Input Tables

Dr. Ejaz Ahmed 41
NULL Search
Example 1: Select all cities
where the number of cars
sold is unkown.
SELECT city
FROM car_sales
WHERE cars_sold IS NULL;
City
Khoba
r
Example 2: Select all cities where
the number of cars sold is kown.
SELECT city
FROM car_sales
WHERE cars_sold IS NOT NULL;
City
Dhahran
Riyadh
Jeddah
Dhahran
Riyadh
Jeddah
Input Tables

Dr. Ejaz Ahmed 42
Removing Duplicate Rows
Example1:
SELECT city
FROM car_sales
Example2:
SELECT DISTINCT city
FROM car_sales
Dhahran
Dhahran
Riyadh
Riyadh
Jeddah
Jeddah
City
Dhahran
Riyadh
Jeddah
City
Using DISTINCT in the SELECT clause removes duplicate rows from the output table
Khobar
Khobar
Input Tables

Dr. Ejaz Ahmed 43
Sorting
• The ORDER BY clause specifies an order
for displaying the result of a query.
– SQL allows the user to order the tuples in the result of a query
by the values of one or more attributes; the default order is
ascending or increasing.
– The keyword DESC is specified to sort in a descending order of
values while the keyword ASC can be used to specify ascending
order explicitly.
– The sorting will be applied alphabetically or numerically
depending on the type of the column attribute.

Dr. Ejaz Ahmed 44
Example: Sorting
Example:
The following SELECT statement
sorts the car_sales table in
ascending order of city and
descending order of car_sales
columns
SELECT *
FROM car_sales
ORDER BY city asc, car_sales desc;
Dhahran
Dhahran
Riyadh
Riyadh
Jeddah
Jeddah
2001
2002
2001
2002
2001
2002
525
456
700
654
921
752
City Year Cars_Sold
Khobar 2002
Input Tables

Dr. Ejaz Ahmed 45
Aggregation …
• ISO standard defines five aggregate functions:
– COUNT returns number of values in a specified
column.
– SUM returns sum of values in a specified column.
– AVG returns average of values in a specified
column.
– MIN returns smallest value in a specified column.
– MAX returns largest value in a specified column.

Dr. Ejaz Ahmed 46
Aggregation …
• Each operates on a single column of a table and return single value.
• COUNT, MIN, and MAX apply to numeric and non-numeric fields, but
SUM and AVG may be used on numeric fields only.
• Apart from COUNT(*), each function eliminates nulls first and
operates only on remaining non-null values.
• COUNT(*) counts all rows of a table, regardless of whether nulls or
duplicate values occur.
• Can use DISTINCT before column name to eliminate duplicates.

Dr. Ejaz Ahmed 47
Aggregation …
• DISTINCT has no effect with MIN/MAX, but may have with
SUM/AVG.
• Aggregate functions can be used only in SELECT list and in HAVING
clause.
• If SELECT list includes an aggregate function and there is no
GROUP BY clause, then SELECT list cannot reference a column with
an aggregate function. For example, following is illegal:
SELECT city, COUNT(*)
FROM car_sales;

Dr. Ejaz Ahmed 48
Example : COUNT
• How many rows
are there in the
car_sales table?
SELECT COUNT(*) as Rows
FROM car_sales
Rows
7
 How many cities are
there in the car_sales
table?
SELECT
COUNT(DISTINCT city)
as city
FROM car_sales
city
4
Input Tables

Dr. Ejaz Ahmed 49
Example : SUM
• Find the total number
of all the cars sold from
the car_sales table?
SELECT
SUM(cars_sold) as cars_sold
FROM car_sales
Cars_sold
4008
 Find the number of all the
cars_sold in Dhahran from the
car_sales table?
SELECT
SUM(cars_sold) as Dah_cars
FROM car_sales
WHERE city = ‘Dhahran’
Dah_cars
981
Input Tables

Dr. Ejaz Ahmed 50
Example: MIN, MAX, AVG
• Find the minimum, maximum, and average cars_sold per year and
per city form the car_sales table
SELECT MIN(cars_sold) as Min_sold
, MAX(cars_sold) as Max_sold
, AVG(cars_sold) as Avg_sold
FROM car_sales
WHERE car_sales IS NOT NULL;
Min_sold Max_sold Avg_sold
456 921 668
Input Tables

Dr. Ejaz Ahmed 51
Grouping
• Use GROUP BY clause to get sub-totals.
• SELECT and GROUP BY closely integrated: each item in SELECT
list must be single-valued per group, and SELECT clause may
only contain:
– Column names.
– Aggregate functions.
– Constants.
– An expression involving combinations of the above.
• All column names in SELECT list must appear in GROUP BY clause
unless name is used only in an aggregate function.
• If WHERE is used with GROUP BY, WHERE is applied first, then
groups are formed from remaining rows satisfying predicate.
• ISO considers two nulls to be equal for purposes of GROUP BY.

Dr. Ejaz Ahmed 52
Example: Grouping
• Find the total cars sold in each city from the car_sales table.
SELECT city, SUM(cars_sold) as
cars
FROM car_sales
WHERE cars_sold IS NOT NULL
GROUP BY city
ORDER BY SUM(cars_sold) ;
City Cars
Dhahran 981
Riyadh 1354
Jeddah 1637
Input Tables

Dr. Ejaz Ahmed 53
Example: Basic Construct of Grouping
• Find the total cars sold in each city from the car_sales table.
City Cars
Dhahran 981
Riyadh 1354
Jeddah 1637
Input Tables

Dr. Ejaz Ahmed 54
Restricting Groups
• HAVING clause is designed for use with GROUP BY clause
to restrict groups that appear in final result table.
• Similar to WHERE, but WHERE filters individual rows
whereas HAVING filters groups.
• Column names in HAVING clause must also appear in the
GROUP BY list or be contained within an aggregate
function.

Dr. Ejaz Ahmed 55
Example: Restricting Groups
• Find the cities who sold a total of more than 1000 cars from the
car_sales table.
SELECT city, SUM(cars_sold) as cars
FROM car_sales
WHERE cars_sold IS NOT NULL
GROUP BY city
HAVING SUM(cars_sold) > 1000 ;
City Cars
Riyadh 1354
Jeddah 1637
Input Tables

Dr. Ejaz Ahmed 56
Aliasing Table Names
• A table alias is created by directly placing an alias after the table
name in the FROM clause.
• The advantage of using a table alias when performing JOIN is
readily apparent when we discuss JOIN later.
• For example in the following example we will refer to departments
table as d or dept.
SELECT d.dname
FROM departments d
WHERE d.dno = 1;
SELECT dept.dname
FROM departments dept
WHERE dept.dno = 1;

Dr. Ejaz Ahmed 57
Nested queries
• Some SQL statements can have a
SELECT embedded within them.
• A subselect can be used in WHERE and
HAVING clauses of an outer SELECT,
where it is called a nested query or a
subquery.
• Subselects may also appear in INSERT,
UPDATE, and DELETEs.

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Example: Nested queries
• From the Lecturer table, select lecturers
whose salary is above average.
• Cannot write 'WHERE salary >
avg(salary)'.
SELECT AVG(salary)
FROM lecturers
SELECT *
FROM lecturers
WHERE salary > (
);
Inner select
Outer select
 The Inner select is done before the outer select.
Input Tables

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Nested query: Example
• List the names of all Lecturers who are in
the ICS department
SELECT lname
FROM lecturers
WHERE dno IN (
);
SELECT dno
FROM department
WHERE dname = ‘ICS’
Input Tables

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Nested Query Rules
• ORDER BY clause may not be used in a subquery (although it may
be used in outermost SELECT).
• Subquery SELECT list must consist of a single column name or
expression, except for subqueries that use EXISTS.
• By default, column names refer to table name in FROM clause of
subquery. Can refer to a table in FROM using an alias.
• When subquery is an operand in a comparison, subquery must
appear on right-hand side.
• A subquery may not be used as an operand in an expression.

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Nested Query: Example
• Find lecturers whose salary higher than
the salary of at least 1 COE lecturer.
SELECT min(salary)
FROM lecturers
WHERE dno = (
)
SELECT *
FROM Lecturers
WHERE salary > (
);
SELECT DNO
FROM department
WHERE dname = ‘COE’
Input Tables

Dr. Ejaz Ahmed 62
Nested Query: Example
• Find lecturers whose salary higher than the salary of every COE lecturer.
SELECT max(salary)
FROM lecturers
WHERE dno = (
)
SELECT *
FROM Lecturers
WHERE salary > (
);
SELECT DNO
FROM department
Input Tables

Dr. Ejaz Ahmed 63
Join
• Can use subqueries provided result columns come from same table.
• If result columns come from more than one table must use a join.
• To perform join, include more than one table in FROM clause.
• Use comma as separator and typically include WHERE clause to
specify join column(s).
• Also possible to use an alias for a table named in FROM clause.
• Alias is separated from table name with a space.
• Alias can be used to qualify column names when there is ambiguity.

Dr. Ejaz Ahmed 64
Example: Join (Inner Join)
• The default type of join is inner join, where arow is included in the
result only if matching row exists in the other relation.
• List each lecturer’s name and his department name.
SELECT a.lname,
b.dname
FROM lecturers a,
departments b
WHERE a.dno = b.dno;
Lname dname
Ahmed
Amin
Hani
Ageel
Yousef
Khalid
ICS
COE
ICS
ICS
COE
COE
Input Tables
PK-FK never makes default join, must
specify Join in SQL

Dr. Ejaz Ahmed 65
Example: Join (Inner Join) …
• To obtain correct rows, include only those
rows from both tables that have identical
values in the dno columns: a.dno = b.dno.
• These two columns are the matching
columns for two tables.
• This type of join is also called inner join
and they equivalent to equi-join in
relational algebra.

Dr. Ejaz Ahmed 66
Computing a Join
• Procedure for generating results of a SELECT with a
join are:
1. Form Cartesian product of the tables named in
FROM clause.
2. If there is a WHERE clause, apply the search
condition to each row of the product table, retaining
those rows that satisfy the condition.
3. For each remaining row, determine the value of each
item in the SELECT list to produce a single row in the
result table.
4. If SELECT DISTINCT has been specified, eliminate
any duplicate rows from the result table.
5. If there is an ORDER BY clause, sort the result table
as required.

Dr. Ejaz Ahmed 67
Outer Joins
• With an inner join, if one row of a table is unmatched,
row is omitted from result table.
• The outer join operations retain rows that do not satisfy
the join condition.
• There are three types of OUTER JOIN
– Left Outer Join
– Right Outer Join
– Full Outer Join
• Lets discuss inner join then we will come back to outer
join.
• Query execution (Performance) is much better than
other joins

Dr. Ejaz Ahmed 68
Outer Join …
• Inner join of departments
and lecturers tables will
result in the following
output.
SELECT a.*, b.*
FROM lecturers a,
Departments b
WHERE a.dno = b.dno
1
2
3
4
5
6
Ahmed
Amin
Hani
Ageel
Yousef
Khalid
1
2
1
1
2
2
4000
3700
4200
4000
3500
4500
1
2
1
1
2
2
dno
ICS
COE
COE
ICS
ICS
COE
dname
Input Tables

Dr. Ejaz Ahmed 69
Outer Join …
• Result table has two rows where the dno
are the same.
• There are no rows corresponding to NW
or Abdella.
• To include unmatched rows in result table,
use an outer join.

Dr. Ejaz Ahmed 70
Example: Left Outer Join
• If We want to Include
in the output table the
lecturers whose
department is unknow
we rewrite our
previous query as
follows
SELECT a.*, b.*
FROM lecturers a,
Departments b
WHERE a.dno = b.dno(+)
1
2
3
5
6
7
Ahmed
Amin
Hani
Ageel
Yousef
Khalid
1
2
1
1
2
2
4000
3700
4200
4000
3500
4500
1
2
1
1
2
2
dno
SE
COE
COE
ICS
SWE
SWE
dname
4 Addella 4300
Input Tables
select d.dname, e.empno, e.ename
from dept d, emp e
where d.deptno=e.deptno(+);

Dr. Ejaz Ahmed 71
Example: Left Outer Join (3-Tables)…

Dr. Ejaz Ahmed 72
Example: Right Outer Join
• If We want to Include
in the output table the
departments with no
lecturers we rewrite
our previous query as
follows
SELECT a.*, b.*
FROM lecturers a,
Departments b
WHERE a.dno (+) = b.dno
1
2
3
5
6
7
Ahmed
Amin
Hani
Ageel
Yousef
Khalid
4
3
1
3
2
2
4000
3700
4200
4000
3500
4500
4
3
1
3
2
2
dno
SE
COE
COE
ICS
SWE
SWE
dname
5 NW
Input Tables

Dr. Ejaz Ahmed 73
Example: Full Outer Join
• If We want to Include in
the output table the
departments with no
lecturers and the
lecturers with unknow
departments we rewrite
our previous query as
follows
SELECT a.*, b.*
FROM lecturers a,
Departments b
WHERE a.dno (+) = b.dno
UNION
SELECT a.*, b.*
FROM lecturers a,
Departments b
WHERE a.dno= b.dno (+);
1
2
3
5
6
7
Ahmed
Amin
Hani
Ageel
Yousef
Khalid
4
3
1
3
2
2
4000
3700
4200
4000
3500
4500
4
3
1
3
2
2
dno
SE
COE
COE
ICS
SWE
SWE
dname
5 NW
4 Abdella 4300
Input Tables

Dr. Ejaz Ahmed 74
Characteristic of Outer Join
• Left Outer Join:
– Includes those rows of first (left) table unmatched with rows from second
(right) table.
– Columns from second table are filled with NULLs.
• Right outer Join :
– includes those rows of second (right) table that are unmatched with rows
from first (left) table.
– Columns from first table are filled with NULLs.
• Full Outer Join:
– Is the UNION of both left and right outer joins.

Dr. Ejaz Ahmed 75
Examples: Left, Right and Full
Outer Joins

Dr. Ejaz Ahmed 76
Union, Intersect, and Difference
• Can use normal set operations of union, intersection,
and difference to combine results of two or more queries
into a single result table.
• Union of two tables, A and B, is table containing all rows
in either A or B or both.
• Intersection is table containing all rows common to both
A and B.
• Difference is table containing all rows in A but not in B.
• Two tables must be union compatible.
• If ALL specified, result can include duplicate rows

Dr. Ejaz Ahmed 77
Example: Use of UNION
• List all the ICS and COE
faculty salaries.
Remove duplicates
SELECT salary
FROM lecturers
WHERE dno = 1
UNION
SELECT salary
FROM lecturers
WHERE dno = 2;
 List all the ICS and COE faculty
salaries. Include duplicates
SELECT salary
FROM lecturers
WHERE dno = 1
UNION ALL
SELECT salary
FROM lecturers
WHERE dno = 2;
Input Tables

Dr. Ejaz Ahmed 78
Example: Use of UNION …
• List all the ICS and COE
faculty salaries. Remove
duplicates
SELECT salary
FROM lecturers
WHERE dno =
( SELECT dno
FROM departments
WHERE dname= ‘ICS’
)
UNION
SELECT salary
FROM lecturers
WHERE dno =
( SELECT dno
FROM departments
WHERE dname= ‘COE’
)
 List all the ICS and COE faculty
salaries. Include duplicates
SELECT salary
FROM lecturers
WHERE dno =
( SELECT dno
FROM departments
WHERE dname= ‘ICS’
)
UNION ALL
SELECT salary
FROM lecturers
WHERE dno =
( SELECT dno
FROM departments
)
Input Tables

Dr. Ejaz Ahmed 79
Example: Use of DIFFERENCE
• List salaries that are taken by ICS and not COE lecturers.
SELECT salary
FROM lecturers
WHERE dno = (
SELECT dno
FROM departments
where dname= ‘ICS’
)
MINUS
SELECT salary
FROM lecturers
WHERE dno = (
SELECT dno
FROM departments
)
Input Tables

Dr. Ejaz Ahmed 80
Example: Use of INTESECTION
• List salaries that are taken by both COE and ICS lecturers.
SELECT salary
FROM lecturers
WHERE dno = (
SELECT dno
FROM departments
where dname= ‘ICS’
)
INTERSECTION
SELECT salary
FROM lecturers
WHERE dno = (
SELECT dno
FROM departments
)
Produces result tables from both
queries and creates single result
table consisting of those rows that
are common to both result tables.
Input Tables

Dr. Ejaz Ahmed 81
Other SQL Operators
• IN (covered)
• BETWEEN (covered)
• LIKE (covered)
• ANY (SOME)
• ALL
• EXISTS
• NOT EXISTS

Dr. Ejaz Ahmed 82
ANY (SOME) and ALL
• ANY and ALL may be used with subqueries that produce a single
column of numbers.
• If subquery preceded by ALL, condition will only be true if it is
satisfied by all values produced by subquery.
• If subquery preceded by ANY, condition will be true if it is satisfied
by any values produced by subquery.
• If subquery is empty, ALL returns true, ANY returns false.
• ISO standard allows SOME to be used in place of ANY.

Dr. Ejaz Ahmed 83
Example using the SOME
Operator
• Find lecturers whose salary higher than
the salary of at least 1 COE lecturer.
SELECT salary
FROM lecturers
WHERE dno = (
)
SELECT *
FROM Lecturers
WHERE salary > SOME (
);
SELECT DNO
FROM department
Input Tables

Dr. Ejaz Ahmed 84
Example Using the ALL
Operator
• Find lecturers whose salary higher than the salary of every COE lecturer.
SELECT salary
FROM lecturers
WHERE dno = (
)
SELECT *
FROM Lecturers
WHERE salary > ALL (
);
SELECT DNO
FROM department

Dr. Ejaz Ahmed 85
EXISTS and NOT EXISTS
• EXISTS and NOT EXISTS are for use only with subqueries specially with
correlated subqueries. A correlated subquery is a subquery where some
attributes of the outer select are used in the inner select.
• They produce a simple true/false result.
• EXISTS is true if and only if there exists at least one row in result table
returned by subquery.
• It is false if subquery returns an empty result table.
• NOT EXISTS is the opposite of EXISTS.
• Since EXISTS and NOT EXISTS check only for existence or non-existence
of rows in subquery result table, subquery can contain any number of
columns.

Dr. Ejaz Ahmed 86
--- Example using the EXISTS
Operator
• Find all ICS lecturers.
SELECT *
FROM lecturers a
WHERE EXISTS
(
SELECT 1
FROM department b
WHERE a.dno = b.dno
AND b.dname = ‘ICS‘
);
Input Tables

Dr. Ejaz Ahmed 87
Example using the NOT
EXISTS Operator
• Find all non ICS
lecturers.
SELECT *
FROM lecturers a
WHERE NOT EXISTS
(
SELECT 1
FROM department b
WHERE a.dno = b.dno
AND b.dname = ‘ICS‘
);

Dr. Ejaz Ahmed 88
More SQL Functions
• SUBSTR
• INSTR
• LENGTH
• LEFT, RIGHT
• LPAD, RPAD
• TRIM
• DECODE
• CEIL
• ROWNUM
TO_CHAR
TO_DATE
TO_NUMBER
ADD_MONTHS
FLOOR
SYSDATE
NVL
TRANSLATE

Dr. Ejaz Ahmed 89
SQL Data Definition Statements
(DDL)
• CREATE SCHEMA and DROP SCEHMA +
• CREATE TABLE +
• ALTER TABLE +
• DROP TABLE +

Dr. Ejaz Ahmed 90
CREATE SCHEMA and DROP
SCHEMA
CREATE SCHEMA [name| AUTHORIZATION creator_id ];
Example: CREATE USER COMPANY IDENTIFIED BY password;
DROP SCHEMA name [RESTRICT | CASCADE ];
Example: DROP USER COMPANY CASCADE;
• With RESTRICT (default), schema must be empty or operation fails.
• With CASCADE, operation cascades to drop all objects associated with
schema in the order defined above. If any of these operations fail, DROP
SCHEMA fails.

Dr. Ejaz Ahmed 91
CREATE TABLE
CREATE TABLE table_name
(col_name data_type [NULL | NOT NULL] [,...]);
• Creates a table with one or more columns of the specified
data_type.
• NULL (default) indicates whether column can contain nulls.
• With NOT NULL, system rejects any attempt to insert a null in the
column.
• Primary keys should always be specified as NOT NULL.
• Foreign keys are often (but not always) candidates for NOT NULL.

Dr. Ejaz Ahmed 92
CREATE TABLE – Example 1
CREATE TABLE Employee
(
fname VARCHAR2(15) NOT NULL,
minit CHAR,
lname VARCHAR2(15) NOT NULL,
ssn CHAR(9),
bdate DATE,
address VARCHAR2(50),
sex CHAR,
salary NUMBER(10,2) NOT NULL,
Superssn CHAR(9),
dno NUMBER(3) NOT NULL,
CONSTRAINT employee_ssn_pk PRIMARY KEY(ssn),
CONSTRAINT employee_superssn_fk
FOREIGN KEY(Superssn) REFERENCES employee(ssn),
CONSTRAINT employee_dno_fk
FOREIGN KEY(dno) REFERENCES department(dnumber),
);

Dr. Ejaz Ahmed 93
CREATE TABLE – Example 2
CREATE TABLE department
(
dname VARCHAR2(15) NOT NULL,
dnumber NUMBER(3) NOT NULL,
mgrssn CHAR(9),
mgrStartDateDATE,
CONSTRAINT department_dnumber_pk
PRIMARY KEY(dnumber),
CONSTRAINT department_mgrssn_fk
FOREIGN KEY(mgrssn) REFERENCES employee(ssn)
);

Dr. Ejaz Ahmed 94
DROP TABLE
DROP TABLE tbl_name [RESTRICT | CASCADE]
e.g. DROP TABLE employee;
• Removes named table and all rows within it.
• With RESTRICT, if any other objects depend for their existence on
continued existence of this table, SQL does not allow request.
• With CASCADE, SQL drops all dependent objects (and objects
dependent on these objects).

Dr. Ejaz Ahmed 95
ALTER TABLE
• The ALTER command is a schema modification command.
• It is used to add or drop a column, change a column definition, add or
drop table constraints.
Examples:
ALTER TABLE COMPANY.EMPLOYEE
MODIFY(lname VARCHAR2(30));
ALTER TABLE EMP
ADD Constraints pk_emp primary key (EMPNO);
ALTER TABLE EMP
ADD CONSTRAINTS FK_DEPTNO FOREIGN KEY (DEPTNO)
REFERENCES DEPT(DEPTNO);

Dr. Ejaz Ahmed 96
SQL Data Manipulation
Statements (DML)
• INSERT Statement +
• UPDATE Statement +
• DELETE Statement +
• Note: Use following control commands for above
SQL
• Commit for DO or confirm
• Rollback for UNDO

Dr. Ejaz Ahmed 97
INSERT Statement
• Definition of INSERT Statement +
• Types of INSERT Statement +
• INSERT and Integrity Constraints +

Dr. Ejaz Ahmed 98
Definition of INSERT Statement
• INSERT is used to add a single row to a
table where we specify the relation name
and a list of values for the row.
• There are three types of INSERT
Statement:
– INSERT With Column list +
– INSERT Without Column list +
– INSERT with SELECT Statement +

Dr. Ejaz Ahmed 99
INSERT with Column list
INSERT INTO table_name (column_list) VALUES
(data_value_list);
• Example: INSERT INTO employee(fname, lname, ssn, salary,
dno)
VALUES (‘Majid', ‘Al-Ghamdi', ‘1111111', 4000,
123);
• data_value_list must match column_list as follows:
– Number of items in each list must be the same.
– Must be direct correspondence in position of items in two lists.
– Data type of each item in data_value_list must be compatible
with data type of corresponding column.
– If one of the table columns is omitted from the column_list It
must also be omitted from the data_value_list and make sure it
is nullable.

Dr. Ejaz Ahmed 100
INSERT without Column List
INSERT INTO table_name VALUES (data_value_list);
• Example: INSERT INTO employee
VALUES (‘Adel', NULL, ‘Al-Eid', ‘222222’,
NULL, NULL, NULL, NULL, NULL, 1);
• data_value_list must match the columns
of the table as follows:
– Number of items in the list must be equal to
the number of columns of the table.
– Data type of corresponding items must be
compatible.

Dr. Ejaz Ahmed 101
INSERT … SELECT
• Second form of INSERT allows multiple rows to
be copied from one or more tables to another:
INSERT INTO table_name [ (column_list) ]
SELECT ...
Example:
INSERT INTO Table1 (A1, A2, A3)
SELECT B1, B2, B3 FROM Table2;

Dr. Ejaz Ahmed 102
INSERT and Integrity
Constraints
• A DBMS that fully implement SQL2 should
support and enforce all the integrity constraints
that can be specified in the DDL.
• A DBMS enforcing NOT NULL will reject an
INSERT command in which an attribute
declared to be NOT NULL does not have a
value.
• A DBMS not supporting referential integrity will
allow insertion even if the referential integrity
constraint is violated.

Dr. Ejaz Ahmed 103
UPDATE
• Definition +
• Examples
– Update All Rows +
– Update Specific Rows +
– Update Multiple Columns +

Dr. Ejaz Ahmed 104
UPDATE Definition …
• The UPDATE command is used to modify attribute values of one or
more selected rows.
UPDATE table_name
SET column_name1 = data_value1
[, column_name2 = data_value2...]
[WHERE search_condition]
• table_name can be name of a base table or an updatable view.
• SET clause specifies names of one or more columns that are to be
updated.

Dr. Ejaz Ahmed 105
UPDATE Definition …
• WHERE clause is optional:
– If omitted, named columns are updated for all
rows in table.
– If specified, only those rows that satisfy
search_condition are updated.
• New data_value(s) must be compatible
with data type for corresponding column.

Dr. Ejaz Ahmed 106
Example: UPDATE All Rows
Give all employees a 3% pay increase.
UPDATE staff
SET salary = salary*1.03;

Dr. Ejaz Ahmed 107
Example: UPDATE Specific
Rows
• Give all Employees in Department one a
5% pay increase.
UPDATE employee
SET salary = salary*1.05
WHERE dno = 1;
• WHERE clause finds rows that contain
data for dno = 1. Update is applied only to
these particular rows.

Dr. Ejaz Ahmed 108
Example: UPDATE Multiple
Columns
• Change Adel’s department to 2 and his
Salary to 4,000. Assume Adel’s ssn =
111;
UPDATE employee
SET dno = 2
, salary = 4000
WHERE ssn = ‘111’;

Dr. Ejaz Ahmed 109
DELETE
• DELETE Definition +
• DELETE Example +

Dr. Ejaz Ahmed 110
DELETE Definition
• A DELETE command removes rows from a table and may include a
where-clause.
• Rows are explicitly deleted from only one table at a time. However,
the deletion may propagate to rows in other tables if referential
triggered actions are specified in the referential integrity constraints
of the DDL.
DELETE FROM table_name [WHERE search_condition]
• table_name can be name of a base table or an updatable view.
• The WHERE clause is optional; if omitted, all rows are deleted from
table. But if it is included only those rows that satisfy the
search_condition are deleted.

Dr. Ejaz Ahmed 111
Example: DELETE
• Delete all records from employee.
DELETE FROM employee;
• Delete all employees in department 1.
DELETE FROM employee
WHERE dno = 1;

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