Constants in PL/SQL

Definition:

• Constants are user defined identifier whose values remain unchanged throughout the program
• Constants needs to be declared prior to their use like variables in PL/SQL
• Constants can declared only in the declaration section in the PL/SQL block.

Syntax:

1. Constant_name CONSTANT data_type(data_width) := value;

Explanation:

•    Constant_name valid constant name (user defined)
•    Constant_name followed CONSTANT keyword
•    Data_type of the value
•    := Assignment operator
•    Value (constant value)

Note: You must initialize the constant at the DECLARATION section. You cannot initialize the constant anywhere else.

Example:

1. DECLARE

      var_pi   CONSTANT NUMBER (7,6) := 3.1415;

   BEGIN

      DBMS_OUTPUT.put_line (var_pi);

   END;

Output:

Attributes of constants:

                 1.    Default

               2.    Not Null

Default:

Here, we are used DEFAULT keyword Instead of assignment operator (:=) for initializing the constant.

1. DECLARE

      var_pi   CONSTANT NUMBER (7, 6) DEFAULT 3.1415;

   BEGIN

      DBMS_OUTPUT.put_line (var_pi);

   END;

Output:

Not Null:

       NOT NULL for preventing Null values.

1. DECLARE

      var_pi   CONSTANT NUMBER (7, 6) NOT NULL DEFAULT 3.1415;

   BEGIN

      DBMS_OUTPUT.put_line (var_pi);

   END;

Output:

Example for Initialize constant in the BEGIN section:

1. DECLARE

      var_pi   CONSTANT NUMBER (7, 6) ;

   BEGIN

      var_pi := 3.1415;

      DBMS_OUTPUT.put_line (var_pi);

   END;

Explanation:

  Above type of declaration and initialization is legally accepted in PL/SQL variable but comes to constant this is not accepted by the compiler.

The error report is,

 

 

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