Declaring PL/SQL Variables.

Declaring PL/SQL Variables:
Syntax
Identifier name [CONSTRAINT] datatype [NOT NULL] [:=DEFAULT]  Expr;
 
Identifier name:

• Specifies the name of the relevant variable for that block.

Constant:

• Constant the variable such that its value cannot change during the program process.
• Constants must be initialized else raise an exception.

Datatype:

• It is a scalar, composite , reference of  LOB data type as applicable to the required situation.

NOTNULL:

• Constraints a variable such that it must contain a value and raises if NULL is identified.
• NOT NULL variables should be initialized else raise an exception.

Default:

• Sets the default value for the value in the PL/SQL program if not attended.

Expr:

• It is any PL/SQL expression that can be a literal, another variable or an expression involving operations and functions for initialization.

Illustration:
 
DECLARE
     Vno number(4):= 7788;
     Vname varchar2(20) not null:=’SCOTT’;
            --must not hold null value through out program
     Doj date default sysdate;
     Flag Boolean:=true;
            --for Boolean variable accept only TRUE or FALSE value and value should not be in single code.
     pcode constant number(6):=567892;
           --cannot be used as an assignment target.