From: | Mike Mascari <mascarm(at)mascari(dot)com> |
---|---|
To: | Mike Mascari <mascarm(at)mascari(dot)com> |
Cc: | Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>, mike(at)linkify(dot)com, pgsql-general(at)postgresql(dot)org |
Subject: | Re: correlated delete with "in" and "left outer join" |
Date: | 2004-02-27 06:49:30 |
Message-ID: | 403EE87A.40405@mascari.com |
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Lists: | pgsql-general |
Mike Mascari wrote:
> Stephan Szabo wrote:
>
>> On Thu, 26 Feb 2004 mike(at)linkify(dot)com wrote:
>>
>>> I'm using postgresl 7.3.2 and have a query that executes very slowly.
>>>
>>> There are 2 tables: Item and LogEvent. ItemID (an int4) is the
>>> primary key
>>> of Item, and is also a field in LogEvent. Some ItemIDs in LogEvent
>>> do not
>>> correspond to ItemIDs in Item, and periodically we need to purge the
>>> non-matching ItemIDs from LogEvent.
>>
>> Perhaps
>> delete from LogEvent where EventType != 'i' and not exists
>> (select * from Item i where i.ItemID=LogEvent.ItemID);
>
>
> Maybe I'm not reading his subquery correctly, but the left outer join
> will produce a row from LogEvent regardless of whether or not a matching
> row exists in Item, correct? So doesn't it reduce to:
>
> DELETE FROM LogEvent WHERE EventType <> 'i';
I failed to read what he was trying to accomplish and assumed the
original query was precisely what he intended. My apologies...
Mike Mascari
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