NVL (expr1, expr2)
NVL2 (expr1, expr2, expr3)
NULLIF (expr1, expr2)
COALESCE (expr1, expr2, ..., exprn)
NVL Converts a null value to an actual value
NVL2 If expr1 is not null, NVL2 returns expr2. If expr1 is null, NVL2 returns expr3. The argument expr1can have any data type.
NULLIF Compares two expressions and returns null if they are equal, or the first expression if they are not equal
COALESCE Returns the first non-null expression in the expression list