Re: RIGHT/FULL OUTER hash joins (was Re: small table left outer join big table)

On Thu, Dec 30, 2010 at 10:45 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I had an epiphany about this topic, or actually two of them.
>
> 1. Whether or not you think there's a significant performance reason
> to support hash right joins, there's a functionality reason.  The
> infrastructure for right join could just as easily do full joins.
> And AFAICS, a hash full join would only require one hashable join
> clause --- the other FULL JOIN ON conditions could be anything at all.
> This is unlike the situation for merge join, where all the JOIN ON
> conditions have to be mergeable or it doesn't work right.  So we could
> greatly reduce the scope of the dreaded "FULL JOIN is only supported
> with merge-joinable join conditions" error.  (Well, okay, it's not
> *that* dreaded, but people complain about it occasionally.)

Yeah, that would be neat.  It might be a lot faster in some cases, too.