testing inequality with columns that can be null

Question

So, I asked a question this morning, which I did not phrase correctly, so I got a lot of responses as to why NULL compared to anything will give NULL/FALSE.

My actual q

Answer 1

If you want to be sure about how NULLs are handled, you'll have to use whatever Informix supports for null checking. I haven't turned up much, other than the SE version doesn't support COALESCE, but it does support DECODE and possibly CASE.

WHERE COALESCE(t.a, 0) != COALESCE(t.b, 0)
WHERE DECODE(NULL, 0, t.a) != DECODE(NULL, 0, t.b)