"Mark Cave-Ayland" <m.cave-ayland@webbased.co.uk> writes:
> ... But in the case of <column> <op>
> <unknown constant>, if we're estimating the number of rows to return then
> that becomes harder
I didn't say it was easy ;-). The existing selectivity functions can't
do better than a rough guess in such cases, and I don't expect you can
either.
regards, tom lane