On Mon, Jun 6, 2016 at 2:53 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Now, if we decide to try to rewrite tlist SRFs as LATERAL, it would likely > behoove us to do that rewrite before expanding * not after, so that we can > eliminate the multiple evaluation of foo() that happens currently. (That > makes it a parser problem not a planner problem.) And maybe we should > rewrite non-SRF composite-returning functions this way too, because people > have definitely complained about the extra evaluations in that context. > But my point here is that lockstep evaluation does have practical use > when the SRFs are iterating over matching collections of generated rows. > And that seems like a pretty common use-case.
Yeah, OK. I'm not terribly opposed to going that way. I think the current behavior sucks badly enough - both because the semantics are bizarre and because it complicates the whole executor for a niche feature - that it's worth taking a backward compatibility hit to change it. I guess I'd prefer #2 to #2.5, #2.5 to #3, and #3 to #1. I really don't like #1 much - I think I'd almost rather do nothing. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
