Re: nullif BUG???

"Josh Berkus" <josh(at)agliodbs(dot)com> writes:
> Er... what were you expecting, exactly?

AFAICT, the quoted behavior is correct per the defined behavior of
nullif(), cf
http://www.ca.postgresql.org/users-lounge/docs/7.1/postgres/functions-conditional.html

NULLIF(value1, value2)

The NULLIF function returns NULL if and only if value1 and
value2 are equal. Otherwise it returns value1.

> Except for IS NULL (and COALESCE, which uses IS NULL) any operation
> involving a NULL is also NULL.

Well, that's not quite the correct reasoning.

NULLIF and COALESCE are both shorthands for CASE expressions, and hence
are capable of returning non-NULL for a NULL input. It all depends on
how the CASE tests are phrased. NULLIF is essentially
CASE WHEN value1 = value2 THEN NULL ELSE value1 END
In the quoted example, "NULL = 5" will yield NULL, which is interpreted
as a FALSE case test, so you get the ELSE case, ie value1, ie NULL.

regards, tom lane