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On 11/22/2012 03:30 AM, Gavin Flower
wrote:
On 22/11/12 04:56, Heikki Linnakangas
wrote:
On
21.11.2012 17:42, Gavin Flower wrote:
On 22/11/12 04:32, Andres Freund wrote:
On 2012-11-21 10:21:16 -0500, Andrew
Dunstan wrote:
I wasn't talking about removing it.
My point was that if the
optimization
fence around CTEs is removed a lot of people will need to
rework apps
where
they have used them for that purpose. And I continue to
think that
spelling
it "OFFSET 0" is horribly obscure.
+1
FWIW, I'm happy with "OFFSET 0". Granted, it's pretty obscure,
but that's what we've historically recommended, and it's pretty
ugly to have to specify a fence like that in the first place.
Whenever you have to resort to it, you ought have a comment in
the query explaining why you need to force the planner like
that, anyway.
WITH foo AS (SELECT ...)
(barrier=on|off)?
9.3 introduces the syntax, defaulting to on
9.4 switches the default to off.
WITH foo AS (SELECT ...) (fence=on|off)?
WITH foo AS (SELECT ...) (optimisation_fence=on|off)?
If we are to invent a new syntax for this, can we please come up
with something that's more widely applicable than just the WITH
syntax. Something that you could use to replace OFFSET 0 in a
subquery, too.
- Heikki
WITH FENCE foo AS (SELECT ...)
default?
That doesn't bind tightly enough to a specific CTE term. Consider:
WITH
FENCE foo AS (SELECT ...),
bar AS (SELECT ...)
SELECT * FROM bar;
Are we fencing just foo? Or all expressions?
--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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