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From: Tom Lane <tgl@sss.pgh.pa.us>
To: pascal+postgres@ensieve.org
cc: pgsql-sql@postgresql.org
Subject: Re: Update Returning as subquery
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Comments: In-reply-to pascal+postgres@ensieve.org
 message dated "Sun, 10 Aug 2014 17:15:20 +0100"
Date: Sun, 10 Aug 2014 13:17:48 -0400
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pascal+postgres@ensieve.org writes:
> Why is that forbidden? Isn't the purpose of a RETURNING clause to return values like a SELECT statement would, and shouldn't it therefore be allowed to occur in the same places?

An INSERT/UPDATE/DELETE RETURNING can be used as a CTE, not as a
sub-select.  Sub-selects aren't sufficiently independent of the outer
query, eg they might be evaluated more than once, or not at all, or
only partially.

			regards, tom lane


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