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Re: offset and limit in update and subselect

From: Lincoln Yeoh <lyeoh(at)pop(dot)jaring(dot)my>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: offset and limit in update and subselect
Date: 2001-02-26 04:39:39
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
At 11:16 PM 25-02-2001 -0500, Tom Lane wrote:
>Right.  Only the first row is locked, but that doesn't help any.  "order
>by random" sounds like it might be a good answer, if there aren't many
>rows that need to be sorted.

Yep. I'll just see what happens in the testing stages.

>> What would happen if I rewrite that query to:
>> update todo set pid = $mypid where exists ( select task id from todo where
>> pid = 0 for update limit 1);
>Right now you get 
>ERROR:  SELECT FOR UPDATE is not allowed in subselects
>This is something that could be fixed if FOR UPDATE were a plan node
>instead of a function done at the executor top level.

OK. Sounds like it won't be worth the trouble to do, plus deadlocks would
be real fun ;).


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