| From: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Rui Carvalho <rui(dot)hmcarvalho(at)gmail(dot)com>, Mike Ivanov <mikei(at)activestate(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: - Slow Query |
| Date: | 2009-07-01 18:00:06 |
| Message-ID: | dcc563d10907011100h55642b96nb6fb3c676fe8b85@mail.gmail.com |
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| Lists: | pgsql-performance |
On Wed, Jul 1, 2009 at 11:52 AM, Tom Lane<tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> writes:
>> Sometimes putting a where clause portion into the on clause helps.
>> like:
>> select * from a left join b on (a.id=b.id) where a.somefield=2
>> might run faster with
>> select * from a left join b on (a.id=bid. and a.somefield=2);
>> but it's hard to say.
>
> Uh, those are not the same query ... they will give different results
> for rows with a.somefield different from 2.
How so? Neither should return any rows with a.somefield <> 2. Or are
you talking where a.somefield is null?
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