Tight Equality / Inequality test taking into account possible NULL values (T-SQL).

Equality test with nulls.sql

-- As suggested in Stackoverflow
-- http://stackoverflow.com/questions/1075142/how-to-compare-values-which-may-both-be-null-is-t-sql
--
-- Equality (true if A & B have same value or both are null):
A = B OR ISNULL(A, B) IS NULL
-- OR
ISNULL(NULLIF(A, B), NULLIF(B, A)) IS NULL

-- Inequaltiy (true if A & B are different and contain null):
ISNULL(NULLIF(A, B), NULLIF(B, A)) IS NOT NULL