"Peter Haworth" <pmh@edison.ioppublishing.com> writes:
> ... why couldn't an explicit IS NULL test
> be allowed to use the index?
It could, if someone cared to puzzle out a way to integrate IS NULL into
the index opclass and access method API infrastructure. Right now all
that stuff assumes that indexable operators are, well, operators (and I
think there are places that assume they must be binary operators, to
boot).
I've looked at this once or twice but always decided that the
bang-for-the-buck ratio was too low compared to other open problems ...
regards, tom lane