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
