Re: wCTE behaviour

From: Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>
To: David Fetter <david(at)fetter(dot)org>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: wCTE behaviour
Date: 2010-11-11 16:50:13
Message-ID: 4CDC1EC5.9050206@cs.helsinki.fi
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On 2010-11-11 6:41 PM +0200, David Fetter wrote:
> On Thu, Nov 11, 2010 at 04:15:34AM +0200, Marko Tiikkaja wrote:
>> The discussion around wCTE during the last week or so has brought to
>> my attention that we don't actually have a consensus on how exactly
>> wCTEs should behave. The question seems to be whether or not a
>> statement should see the modifications of statements ran before it.
>> While I think making the modifications visible would be a lot more
>> intuitive, it's not clear how we'd optimize the execution in the
>> future without changing the behaviour (triggers are a big concern).
>
> +1 for letting writeable CTEs see the results of previous CTEs, just
> as current non-writeable ones do. A lot of the useful cases for this
> feature depend on this visibility.

Just to be clear, the main point is whether they see the data
modifications or not. The simplest case to point out this behaviour is:

WITH t AS (DELETE FROM foo)
SELECT * FROM foo;

And the big question is: what state of "foo" should the SELECT statement
see?

Regards,
Marko Tiikkaja

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