Oracle

Oracle for
Beginners
BY: Jigar M.

What is Oracle
– Oracle database is a relational database management system. It is known as
Oracle database, Oracle DB or simply Oracle. It is produced and marketed by
Oracle Corporation.
– Oracle database is the first database designed for enterprise grid computing.
The enterprise grid computing provides the most flexible and cost effective way
to manage information and applications.

Different editions of Oracle
database
Following are the four editions of the Oracle database.
– Enterprise Edition: It is the most robust and secure edition. It offers all features,
including superior performance and security.
– Standard Edition: It provides the base functionality for users that do not require
Enterprise Edition's robust package.
– Express Edition (XE): It is the lightweight, free and limited Windows and Linux
edition.
– Oracle Lite: It is designed for mobile devices

Introduction to Oracle Datatypes
– Oracle provides the following categories of built-in datatypes:
– Overview of Character Datatypes
– Overview of Numeric Datatypes
– Overview of DATE Datatype
– Overview of LOB Datatypes

Overview of Character
Datatypes
– The character datatypes store character (alphanumeric) data in strings, with
byte values corresponding to the character encoding scheme, generally called a
character set or code page.
– The database's character set is established when you create the database.
Examples of character sets are 7-bit ASCII (American Standard Code for
Information Interchange), EBCDIC (Extended Binary Coded Decimal Interchange
Code), Code Page 500, Japan Extended UNIX, and Unicode UTF-8. Oracle
supports both single-byte and multibyte encoding schemes.

CHAR Datatype
– The CHAR datatype stores fixed-length character strings. When you create a
table with a CHAR column, you must specify a string length (in bytes or
characters) between 1 and 2000 bytes for the CHAR column width. The default
is 1 byte. Oracle then guarantees that:
 When you insert or update a row in the table, the value for the CHAR column has the
fixed length.
 If you give a shorter value, then the value is blank-padded to the fixed length.
 If a value is too large, Oracle Database returns an error.

VARCHAR2 and VARCHAR
Datatypes
– The VARCHAR2 datatype stores variable-length character strings. When you create a
table with a VARCHAR2 column, you specify a maximum string length (in bytes or
characters) between 1 and 4000 bytes for the VARCHAR2 column. For each row,
Oracle Database stores each value in the column as a variable-length field unless a
value exceeds the column's maximum length, in which case Oracle Database returns
an error. Using VARCHAR2 and VARCHAR saves on space used by the table.
– For example, assume you declare a column VARCHAR2 with a maximum size of 50
characters. In a single-byte character set, if only 10 characters are given for the
VARCHAR2 column value in a particular row, the column in the row's row piece
stores only the 10 characters (10 bytes), not 50.

VARCHAR Datatype
– The VARCHAR datatype is synonymous with the VARCHAR2 datatype. To avoid
possible changes in behavior, always use the VARCHAR2 datatype to store
variable-length character strings.

NCHAR and NVARCHAR2
Datatypes
– NCHAR and NVARCHAR2 are Unicode datatypes that store Unicode character
data. The character set of NCHAR and NVARCHAR2 datatypes can only be either
AL16UTF16 or UTF8 and is specified at database creation time as the national
character set. AL16UTF16 and UTF8 are both Unicode encoding.
 The NCHAR datatype stores fixed-length character strings that correspond to the
national character set.
 The NVARCHAR2 datatype stores variable length character strings.

Contd.
NCHAR
– The maximum length of an NCHAR column is 2000 bytes. It can hold up to 2000
characters. The actual data is subject to the maximum byte limit of 2000. The
two size constraints must be satisfied simultaneously at run time.
NVARCHAR2
– The maximum length of an NVARCHAR2 column is 4000 bytes. It can hold up to
4000 characters. The actual data is subject to the maximum byte limit of 4000.
The two size constraints must be satisfied simultaneously at run time.

LOB Character Datatypes
– The LOB datatypes for character data are CLOB and NCLOB. They can store up to
8 terabytes of character data (CLOB) or national character set data (NCLOB).
Note:
– Do not create tables with LONG columns. Use LOB columns (CLOB, NCLOB) instead.
LONG columns are supported only for backward compatibility.
– Oracle also recommends that you convert existing LONG columns to LOB columns.
LOB columns are subject to far fewer restrictions than LONG columns. Further, LOB
functionality is enhanced in every release, whereas LONG functionality has been
static for several releases

LONG Datatype
– Columns defined as LONG can store variable-length character data containing
up to 2 gigabytes of information. LONG data is text data that is to be
appropriately converted when moving among different systems.
– LONG datatype columns are used in the data dictionary to store the text of view
definitions. You can use LONG columns in SELECT lists, SET clauses of UPDATE
statements, and VALUES clauses of INSERT statements.

Overview of Numeric Datatypes
– The numeric datatypes store positive and negative fixed and floating-point
numbers, zero, infinity, and values that are the undefined result of an operation
(that is, is "not a number" or NAN).
– This section includes the following topics:
– NUMBER Datatype
– Floating-Point Numbers

NUMBER Datatype
– The NUMBER datatype stores fixed and floating-point numbers. Numbers of
virtually any magnitude can be stored and are guaranteed portable among
different systems operating Oracle Database, up to 38 digits of precision.
– For numeric columns, you can specify the column as:
– column_name NUMBER
– Optionally, you can also specify a precision (total number of digits) and scale
(number of digits to the right of the decimal point):
– column_name NUMBER (precision, scale)

Floating-Point Numbers
– Oracle Database provides two numeric datatypes exclusively for floating-point
numbers: BINARY_FLOAT and BINARY_DOUBLE.
– BINARY_FLOAT Datatype
– BINARY_DOUBLE Datatype

Contd
BINARY_FLOAT Datatype
– BINARY_FLOAT is a 32-bit, single-precision floating-point number datatype. Each
BINARY_FLOAT value requires 5 bytes, including a length byte.
BINARY_DOUBLE Datatype
– BINARY_DOUBLE is a 64-bit, double-precision floating-point number datatype.
Each BINARY_DOUBLE value requires 9 bytes, including a length byte.

Overview of DATE Datatype
– The DATE datatype stores point-in-time values (dates and times) in a table. The
DATE datatype stores the year (including the century), the month, the day, the
hours, the minutes, and the seconds (after midnight).
– For input and output of dates, the standard Oracle date format is DD-MON-YY,
as follows:'13-NOV-92'
– You can change this default date format for an instance with the parameter
NLS_DATE_FORMAT.
– TO_DATE ('November 13, 1992', 'MONTH DD, YYYY')

Time Zones
Datatype Time Zone Fractional Seconds
DATE No No
TIMESTAMP No Yes
TIMESTAMP WITH TIME
ZONE
Explicit Yes
TIMESTAMP WITH LOCAL
TIME ZONE
Relative Yes

Overview of LOB Datatypes
– The LOB datatypes BLOB, CLOB, NCLOB, and BFILE enable you to store and manipulate large blocks
of unstructured data (such as text, graphic images, video clips, and sound waveforms) in binary or
character format.
– LOB datatypes differ from LONG and LONG RAW datatypes in several ways. For example:
 A table can contain multiple LOB columns but only one LONG column.
 A table containing one or more LOB columns can be partitioned, but a table containing a LONG column cannot
be partitioned.
 The maximum size of a LOB is 128 terabytes depending on database block size, and the maximum size of a
LONG is only 2 gigabytes.
 LOBs support random access to data, but LONGs support only sequential access.
 LOB datatypes (except NCLOB) can be attributes of a user-defined object type but LONG datatypes cannot.
 Tables with LOB columns can be replicated, but tables with LONG columns cannot.

Contd
– SQL statements define LOB columns in a table and LOB attributes in a user-defined
object type. When defining LOBs in a table, you can explicitly specify the tablespace
and storage characteristics for each LOB.
– LOB datatypes can be stored inline (within a table), out-of-line (within a tablespace,
using a LOB locator), or in an external file (BFILE datatypes). With compatibility set
to Oracle9i or higher, you can use LOBs with SQL VARCHAR operators and functions.
 BLOB Datatype
 CLOB and NCLOB Datatypes
 BFILE Datatype

BLOB Datatype
– The BLOB datatype stores unstructured binary data in the database. BLOBs can
store up to 128 terabytes of binary data.
– BLOBs participate fully in transactions. Changes made to a BLOB value by the
DBMS_LOB package, PL/SQL, or the OCI can be committed or rolled back.
However, BLOB locators cannot span transactions or sessions.

CLOB and NCLOB Datatypes
– The CLOB and NCLOB datatypes store up to 128 terabytes of character data in the
database. CLOBs store database character set data, and NCLOBs store Unicode
national character set data. Storing varying-width LOB data in a fixed-width Unicode
character set internally enables Oracle Database to provide efficient character-
based random access on CLOBs and NCLOBs.
– CLOBs and NCLOBs participate fully in transactions. Changes made to a CLOB or
NCLOB value by the DBMS_LOB package, PL/SQL, or the OCI can be committed or
rolled back. However, CLOB and NCLOB locators cannot span transactions or
sessions. You cannot create an object type with NCLOB attributes, but you can
specify NCLOB parameters in a method for an object type.

BFILE Datatype
– The BFILE datatype stores unstructured binary data in operating-system files
outside the database. A BFILE column or attribute stores a file locator that
points to an external file containing the data. The amount of BFILE data that can
be stored is limited by the operating system.
– BFILEs are read only; you cannot modify them. They support only random (not
sequential) reads, and they do not participate in transactions. The underlying
operating system must maintain the file integrity, security, and durability for
BFILEs. The database administrator must ensure that the file exists and that
Oracle Database processes have operating-system read permissions on the file.

Oracle CREATE TABLE
CREATE TABLE table_name
(
column1 datatype [ NULL | NOT NULL ],
column2 datatype [ NULL | NOT NULL ],
...
column_n datatype [ NULL | NOT NULL ]
);
– table_name: It specifies the name of
the table which you want to create.
– column1, column2, ... column n: It
specifies the columns which you want
to add in the table. Every column must
have a datatype. Every column should
either be defined as "NULL" or "NOT
NULL". In the case, the value is left
blank; it is treated as "NULL" as default.

What is Primary key
– A primary key is a single field or combination of fields that contains a unique
record. It must be filled. None of the field of primary key can contain a null
value. A table can have only one primary key.
– Oracle CREATE TABLE Example with primary key
CREATE TABLE customers
( customer_id number(10) NOT NULL,
customer_name varchar2(50) NOT NULL,
city varchar2(50),
CONSTRAINT customers_pk PRIMARY KEY (customer_id)
);

Oracle ALTER TABLE
Statement
– In Oracle, ALTER TABLE statement specifies how to add, modify, drop or delete
columns in a table. It is also used to rename a table
– How to add column in a table
ALTER TABLE table_name ADD column_name column-definition;
Example:
ALTER TABLE customers ADD customer_age varchar2(50);
– How to modify multiple columns of a table
ALTER TABLE table_name MODIFY (column_1 column_type,
column_2 column_type, ...
column_n column_type);

How to drop column of a table
Syntax
– ALTER TABLE table_name DROP COLUMN column_name;
Example
– ALTER TABLE customers DROP COLUMN customer_name;

How to rename column of a table
Syntax
– ALTER TABLE table_name RENAME COLUMN old_name to new_name;
Example
– ALTER TABLE customers RENAME COLUMN customer_name to cname;

How to rename table
Syntax
– ALTER TABLE table_name RENAME TO new_table_name;
Example
– ALTER TABLE customers RENAME TO retailers;

Oracle

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