SQL Language Extension: NULLIF Function: Return a NULL value for a sub-expression if it has a specific value otherwise return the value of the sub-expression Author: Arno Brinkman <firebird@abvisie.nl> Format: <case abbreviation> ::= NULLIF <left paren> <value expression> <comma> <value expression> <right paren> Syntax Rules: 1) NULLIF (V1, V2) is equivalent to the following <case specification>: CASE WHEN V1 = V2 THEN NULL ELSE V1 END Notes: See also README.data_type_results_of_aggregations.txt Examples: A) UPDATE PRODUCTS SET STOCK = NULLIF(STOCK,0)