From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | PG Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | DECLARE CURSOR must not contain data-modifying statements in WITH |
Date: | 2011-09-21 16:19:43 |
Message-ID: | 201109211819.44027.andres@anarazel.de |
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Lists: | pgsql-hackers |
Hi all,
Whats the reason for disallowing cursors on wCTEs? I am not sure I can follow
the comment:
/*
* We also disallow data-modifying WITH in a cursor. (This could be
* allowed, but the semantics of when the updates occur might be
* surprising.)
*/
if (result->hasModifyingCTE)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("DECLARE CURSOR must not contain data-modifying
statements in WITH")));
Given that cursors are about the only sensible way to return larger amounts of
data, that behaviour reduces the usefulness of wCTEs a bit.
Whats the exact cause of concern here? I personally don't think there is a
problem documenting that you should fetch the cursor fully before relying on
the updated tables to be in a sensible state. But that may be just me.
Thanks,
Andres
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