NULL comparison, take 2

Question

Hello all,

I have a subquery, used in WHERE section:

A.column <> B.column

Unfortunately, it doesn't work, if either A.column or B.column is NULL. So, I converted it to:

((A.column <> B.column) OR ((A.column IS NULL) <> (B.column IS NULL)))

, presuming that "Table.column IS NULL" is boolean value and I can compare 2 boolean values. But...

Incorrect syntax near '<'.

I don't like

((A.column <> B.column) OR ((A.column IS NULL) AND (B.column IS NOT NULL)) OR
((A.column IS NOT NULL) AND (B.column IS NULL)))

How could I workarounf this?

Regards,

Answer 1

Use ISNULL function.

Answer 2

(ISNULL(A.column,0)) <> (ISNULL(B.column,0))

Answer 3

NULLIF yields null when two values are equal =)

WHERE NULLIF(A.column, B.column) IS NOT NULL