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Re: BUG #3052: Inconsistent results from PQexec... with rules

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "brian blakey" <bmb4605(at)yahoo(dot)co(dot)uk>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #3052: Inconsistent results from PQexec... with rules
Date: 2007-02-23 16:06:33
Message-ID: 27359.1172246793@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-bugs
"brian blakey" <bmb4605(at)yahoo(dot)co(dot)uk> writes:
> Shouldn't all three PQexec... functions return the same results for
> equivalent requests.

No, because they're using different underlying protocols with different
feature sets.  AFAICT you do get back "INSERT 0 0" command status in
both cases, but the non-PQexec functions are using extended query
protocol which will not return tuples for a non-SELECT query.  There's
a relevant comment in PortalRunMulti:

    /*
     * If the destination is DestRemoteExecute, change to DestNone.  The
     * reason is that the client won't be expecting any tuples, and indeed has
     * no way to know what they are, since there is no provision for Describe
     * to send a RowDescription message when this portal execution strategy is
     * in effect.  This presently will only affect SELECT commands added to
     * non-SELECT queries by rewrite rules: such commands will be executed,
     * but the results will be discarded unless you use "simple Query"
     * protocol.
     */

The old simple-Query protocol is fairly laid back about this, and can
indeed tolerate several SELECTs with different row descriptors generated
from a single command.  (Although PQexec has its own limitations, and
will summarily discard all but the last one...)  The newer protocol is
designed to be a lot more predictable from the client's point of view,
so it won't allow that.

			regards, tom lane

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