Re: Posible planner improvement?

[Mark Mielke <mark(at)mark(dot)mielke(dot)cc>]

A Dimecres 21 Maig 2008, Richard Huxton va escriure:
> > Albert Cervera Areny wrote:
> >     
> > > I've got a query similar to this:
> > >
> > > select * from t1, t2 where t1.id > 158507 and t1.id = t2.id;
> > >
> > > That took > 84 minutes (the query was a bit longer but this is the part
> > > that made the difference) after a little change the query took ~1 second:
> > >
> > > select * from t1, t2 where t1.id > 158507 and t2.id > 158507 and t1.id =
> > > t2.id;
> > >       
> > Try posting EXPLAIN ANALYSE SELECT ... for both of those queries and
> > we'll see why it's better at the second one.
> >     

Even if the estimates were off (they look a bit off for the first 
table), the above two queries are logically identical, and I would 
expect the planner to make the same decision for both.

I am curious - what is the result of:

   select * from t1, t2 where t2.id > 158507 and t1.id = t2.id;

Is it the same speed as the first or second, or is a third speed entirely?

If t1.id = t2.id, I would expect the planner to substitute them freely 
in terms of identities?

Cheers,
mark

--
Mark Mielke <mark(at)mielke(dot)cc>