NULLIF

The Oracle and PL/SQL NULLIF function compares expr1 and expr2. If they are equal, then the function returns null. If they are not equal, then the function returns expr1.

The general format is:

NULLIF(expr1, expr2)

You cannot specify the literal NULL for expr1 but can be an expression that evaluates to NULL.

Example 1:

SELECT NULLIF('pear','apple') FROM DUAL;

returns:

pear

Example 2:

SELECT NULLIF('apple','apple') FROM DUAL;

returns:

NULL