PROGRAMMER-DEFINED TYPES

With the SUBTYPE statement, PL/SQL allows you to define your own subtypes or aliases of predefined datatypes, sometimes referred to as abstract datatypes.

There are two kinds of subtypes.

Ø  Constrained

Ø  Unconstrained

CONSTRAINED SUBTYPE

A subtype that restricts or constrains the values normally allowd by the datatype itself.

Ex:

            Subtype positive is binary_integer range 1..2147483647;

In the above declaration a variable that is declared as positive can store only ingeger greater than zero even though binary_integer ranges from -2147483647..+2147483647.

UNCONSTRAINED SUBTYPE

A subtype that does not restrict the values of the original datatype in variables declared with the subtype.

Ex:

            Subtype float is number;