From: Tambet Matiisen <t.matiisen@aprote.ee>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: KÖPFERL Robert <robert.koepferl@sonorys.at>
Cc: pgsql-sql@postgresql.org
Subject: Re: Function to either return one or all records
Date: Thu, 21 Apr 2005 10:34:33 +0300
Message-ID: <A66A11DBF5525341AEF6B8DE39CDE7700729EC@black.aprote.com> (raw)
> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> Sent: Thursday, April 21, 2005 12:06 AM
> To: Tambet Matiisen
> Cc: KÖPFERL Robert; pgsql-sql@postgresql.org
> Subject: Re: [SQL] Function to either return one or all records
>
>
> "Tambet Matiisen" <t.matiisen@aprote.ee> writes:
> > Standard technique is to rewrite OR queries to UNION queries. I
> > believe PostgreSQL optimizer does not do that automatically. So you
> > could try instead:
>
> > select * from id_bal_tbl where $1 is null
> > union all
> > select * from id_bal_tbl where id = $1;
>
> ... but that won't do anything to solve the performance
> problem. Doesn't help for the second select to use an index,
> if the first one grovels over the whole table anyway ...
>
Hmm, I tought about that before sending mail to list and did a little test. My test indicated, that the seq scan was discarded, it was definitely faster than OR query. I couldn't verify plan, as EXPLAIN shows only function scan.
Tambet
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To: pgsql-sql@postgresql.org
Cc: t.matiisen@aprote.ee, tgl@sss.pgh.pa.us, robert.koepferl@sonorys.at
Subject: Re: Function to either return one or all records
In-Reply-To: <A66A11DBF5525341AEF6B8DE39CDE7700729EC@black.aprote.com>
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