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Re: Delete performance

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Phillip Sitbon <phillip(at)sitbon(dot)net>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: Delete performance
Date: 2009-06-15 18:46:52
Message-ID: 21389.1245091612@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-novice
Phillip Sitbon <phillip(at)sitbon(dot)net> writes:
> I've had to do this quite a bit, and here's how I usually go about it:

> DELETE FROM data_structures_items WHERE NOT EXISTS
>   (SELECT 1 FROM data_structures WHERE id_structure=id_data_structure LIMIT 1);

> Even when the item in the subquery is a primary key, I find it
> semantically informative to always use "LIMIT 1".

EXISTS implies LIMIT 1 for its subquery; there's no value for either
comprehension or performance in adding that.  I'd recommend leaving
it off, because it makes your query syntax nonstandard for no benefit.

			regards, tom lane

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