Re: Recognizing range constraints (was Re: Plan for relatively simple query seems to be very inefficient)

Quoting Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> Mischa <mischa(dot)Sandberg(at)telus(dot)net> writes:
> > Quoting Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> >> WHERE a.x > b.y AND a.x < 42
>
> > Out of curiosity, will the planner induce "b.y < 42" out of this?
>
> No. There's some smarts about transitive equality, but none about
> transitive inequalities. Offhand I'm not sure if it'd be useful to add
> such. The transitive-equality code pulls its weight [...]
> but I'm less able to think of common use-cases for transitive
> inequality ...

Thanks. My apologies for not just going and looking at the code first.

Equality-transitives: yes, worth their weight in gold.
Inequality-transitivies: I see in OLAP queries (usually ranges), or in queries
against big UNION ALL views, where const false inequalities are the norm.
"a.x > b.y and a.x < c.z" comes up in OLAP, too, usually inside an EXISTS(...),
where you are doing something analogous to finding a path.