On Thu, May 4, 2017 at 9:22 AM, Andrew Dunstan < andrew.duns...@2ndquadrant.com> wrote:
> > Yeah, the idea that this won't cause possibly significant pain is quite > wrong. Quite by accident I came across an example just this morning where > rewriting as a CTE makes a big improvement. > > I wrote this query: > > select (json_populate_record(null::mytype, myjson)).* > from mytable; > > > It turned out that this was an order of magnitude faster: > > with r as > ( > select json_populate_record(null::mytype, myjson) as x > from mytable > ) > select (x).* > from r; > ​Except I suspect we at least have a chance to detect the above and not de-optimize it by evaluating "json_populate_record" once for every column in mytype. The now idiomatic solution​ to the above is to use LATERAL so the above CTE is no longer actually a required workaround. David J.
