On Tue, Nov 20, 2012 at 5:24 PM, Merlin Moncure <[email protected]> wrote: > On Tue, Nov 20, 2012 at 1:53 PM, Jon Nelson <[email protected]> wrote: >> As can be seen by the current conversation, not everyone is convinced > that CTEs ought to be an explicit optimization barrier > > On Tue, Nov 20, 2012 at 1:26 PM, Claudio Freire <[email protected]> > wrote: >> It *could* just be a lack of imagination on my part. But if it were >> not, then it'd be nice for it to be done automatically (since this >> particular CTE behavior bites enough people already). > > Sure. I just find it personally hard to find a good demarcation line > between A: "queries where pushing quals through are universally > beneficial and wanted" and B: "queries where we are inserting an > explicit materialization step to avoid planner issues", particularly > where there is substantial overlap with between A and C: "queries that > are written with a CTE and arguably shouldn't be". > > Put another way, I find CTE to express: 'this then that' where joins > express 'this with that'. So current behavior is not surprising at > all. All that said, there could be a narrow class of low hanging cases > (such as the OP's) that could be sniped...I'm just skeptical.
It could work very well towards CTE-including views, where the quals cannot be added in the view but would be present when the view is expanded in final queries. -- Sent via pgsql-performance mailing list ([email protected]) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
