NULLIF-----------------------------------------------------------------------------------

SQL> select nullif(2,20) from dual;

NULLIF(2,20)
------------
2

if arg1 <> arg2 return arg1

SQL> select nullif(2,20) from dual;

NULLIF(2,20)
------------

if arg1 = arg2 return null

NVL--------------------------------------------------------------------------------------------
SQL> select nvl(null,30 ) from dual;

NVL(NULL,30)
------------
30

SQL> select nvl(2,30) from dual;

NVL(2,30)
----------
2

if arg1 is null then return arg2 else arg1

NVL2----------------------------------------------------------------------------------------

SQL> select nvl2(null,2,3) from dual;

NVL2(NULL,2,3)
--------------
3

SQL> select nvl2(1,2,3) from dual;

NVL2(1,2,3)
-----------
2

if arg1 is null then return arg3 else arg2

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nvl nvl nullif