Re: [SQL] Good Optimization

secret <secret(at)kearneydev(dot)com> writes:
> There is a simple way to optimize SQL queries involving joins to
> PostgreSQL that I think should be handled by Postgre? If one is joining
> a tables a,b on attribute "x" and if one has something like x=3 then it
> helps A LOT to say: a.x=3 and b.x=3 in addition to saying a.x=b.x ...
> The example below shoulds the radical speed gain of doing this, and I
> think it isn't something real obvious to most people...

How much *actual* speedup is there? I don't trust the optimizer's
numbers as anything more than relative measures ;-)

I'm a bit surprised that you are getting a nested-loop plan and not
a merge or hash join. With a merge join, at least, there ought not be
a large difference from providing the additional qual clause (I think).
What Postgres version are you using?

regards, tom lane