Oracle Advanced PL/SQL Developer Professional Guide

Functions

Like a procedure, a function is also a derivative of a PL/SQL block structure which is physically stored within a database. Unlike procedures, they are the "workforce" in PL/SQL and meant for calculative and computational activities in the applications.

The characteristics of functions are as follows:

• Functions can be called from SQL statements (SELECT and DMLs). Such functions must accept only IN parameters of valid SQL types. Alternatively, a function can also be invoked from SELECT statements if the function body obeys the database purity rules.
• Functions can accept parameters in all three modes (IN, OUT, and IN OUT) and mandatorily return a value. The type of the return value must be a valid SQL data type (not be of BOOLEAN, RECORD ...