This function returns the value NULL, if two expressions are identical. Otherwise, the first expression is returned.
NULL
nullif::=
The NULLIF function is equivalent to the CASE expression CASE WHEN expr1=expr2 THEN NULL ELSE expr1 END.
NULLIF
CASE
CASE WHEN expr1=expr2 THEN NULL ELSE expr1 END
SELECT NULLIF(1,2) NULLIF1, NULLIF(1,1) NULLIF2;
