"Karl O. Pinc" <kop(at)meme(dot)com> writes:
> But SQL has 3 valued logic (strictly speaking, not boolean). It
> seems that the CHECK clases fail only when the expression result
> is FALSE, and pass when the result is either TRUE or UNKNOWN.
Correct --- this is per spec.
> Yes? Should this be clarified in the documentation?
Sure, send a documentation patch.
regards, tom lane