Re: [HACKERS] Idea for speeding up uncorrelated subqueries

> Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> writes:
> >> Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> writes:
> >>>> Yes, the subqueries need work. We don't even do index lookups into the
> >>>> inner plan, only sequential. Already on TODO.
> >>
> >> Huh? I don't follow that at all...
>
> > Suppose you have a subquery that returns 1000 rows. There is no code so
> > lookups of the inner table are indexed:
>
> > select *
> > from tab
> > where col in (select col2 from tab2)
>
> > In this case, a sequential scan of the subquery results are required.
>
> Well, yes, the subquery is a sequential scan. I guess what you are
> envisioning is rewriting this into some kind of nested-loop join?
> For simple cases that might be possible...

Yes, or mergejoin/hashjoin.

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