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.
>>The query is:
>>delete from LogEvent where EventType != 'i' and ItemID in
>>(select distinct e.ItemID from LogEvent e left outer join Item i
>>on e.ItemID = i.ItemID where e.EventType != 'i' and i.ItemID is null);
>>I understand that using "in" is not very efficient.
>>Is there some other way to write this query without the "in"?
> 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';
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