On 11 November 2010 16:50, Marko Tiikkaja
<marko.tiikkaja@cs.helsinki.fi> wrote:
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?
I would expect that select to return nothing. And if the user wished to reference what was deleted, they could use RETURNING anyway. </probable ignorance>
WITH t AS (UPDATE foo SET col = true)
SELECT * FROM foo WHERE col = false;
... Wouldn't this be more practical to have foo's UPDATEs applied prior to SELECT? Otherwise what would the usecase be?
--
Thom Brown
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