NULLIF (a, b): if (a=b) then NULL else a NVL (a, b): if (a IS NULL) then b else a NVL2 (a, b, c): if (a IS NULL) then b else c DECODE (exp, srch1, rslt1, srch2, rslt2, …, default): if (exp = srch1) then rslt1 else if (exp = srch2) then rslt2 … ……