Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> I thought NOT IN was the only one that was concerned about any NULL?
No, they both are: in the presence of NULLs, IN can return TRUE or NULL,
NOT IN can return FALSE or NULL.
The reason the FAQ is always about NOT NULL is that WHERE treats NULL as
FALSE, so the average newbie writing an IN doesn't even realize he's
getting a NULL rather than a FALSE. With NOT NULL, he can't ignore it.
regards, tom lane