| From: | nolan(at)celery(dot)tssi(dot)com |
|---|---|
| To: | swampler(at)noao(dot)edu (Steve Wampler) |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Improving a simple query? |
| Date: | 2003-07-14 01:23:47 |
| Message-ID: | 20030714012347.18920.qmail@celery.tssi.com |
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| Thread: | |
| Lists: | pgsql-performance |
> > Could you not rewrite this as a simple join though?
>
> Hmmm, I don't see how. Then again, I'm pretty much the village
> idiot w.r.t. SQL...
>
> The inner select is locating a set of (2049) ids (actually from
> the same table, since 'attributes' is just a view into
> 'attributes_table'). The outer select is then locating all
> records (~30-40K) that have any of those ids. Is that really
> something a JOIN could be used for?
This may be a question for SQL theoretists, but I don't think I've ever
run across a query with a 'where in' clause that couldn't be written
as a join. I think linguistically 'where in' may even be a special
case of 'join'.
Yet another question for the theoretists: Would it be possible to optimize
a 'where in' query by rewriting it as a join?
--
Mike Nolan
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