DECODE

DECODE is a single-row function in Oracle, which applies conditional logic to SQL queries. This function works very much like an IF-THEN-ELSE statement.

Syntax: DECODE (expression1, value1, return_value1, value2, return_value2, ... valueN, return_valueN, [default_return_value] )

How it works

If expression1 equals value1 then return_value1 is returned by DECODE function, and if expression1 equals value2 then return_value2 is returned and so on…..

The optional default_return_value is returned if expression1 does not match with any of (value1, value2, ..., valueN).

In short

IF expression1 = valueN THEN return_valueN ELSE default_return_value

Example: DECODE (day_id, '1', 'Monday', '2', 'Tuesday', .... '7', 'Sunday', 'Not Valid')