On Sat, Jul 24, 2021 at 10:14 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > > Andy Fan <zhihui.fan1...@gmail.com> writes: > > When I am working on the UnqiueKey stuff, I find the following cases. > > SELECT * FROM (SELECT * FROM t offset 0) v ORDER BY a; > > // root->query_keys = A. root->order_pathkeys = A > > // Current: subroot->query_pathkeys = NIL. > > // Expected: subroot->xxxx_pathkeys = [A]. > > Why do you "expect" that? I think pushing the outer ORDER BY past a > LIMIT is an unacceptable semantics change. > > regards, tom lane
I don't mean push down a "ORDER BY" clause to subquery, I mean push down an "interesting order" to subquery. for example we have index t(a); then SELECT * FROM (SELECT a FROM t OFFSET 0) v ORDER BY a; In the current implementation, when we are planning the subuqery, planners think the "pathkey a" is not interesting, but it should be IIUC. -- Best Regards Andy Fan (https://www.aliyun.com/)
