>>>>> "Tom" == Tom Lane <t...@sss.pgh.pa.us> writes:
Tom> After further reflection I really don't like Andrew's suggestion Tom> that we not document the rule that multiply-referenced CTEs won't Tom> be inlined by default. That would be giving up the principle that Tom> WITH calculations are not done multiple times by default, and I Tom> draw the line at that. It's an often-useful behavior as well as Tom> one that's been documented from day one, so I do not accept the Tom> argument that we might someday override it on the basis of nothing Tom> but planner cost estimates. The case that springs to mind is when a CTE with grouping is then joined multiple times in the main query with different conditions. If the planner is able to deduce (e.g. via ECs) that restrictions on grouped columns can be pushed into the CTE, then inlining the CTE multiple times might be a significant win. But if that isn't possible, then inlining multiple times might be a significant loss. If such a query is made into a view, then (given your position) the decision of whether to inline has to be made at view creation time, which doesn't seem desirable (even if we have to put up with it for the present). -- Andrew (irc:RhodiumToad)