On Wed, 2019-11-27 at 08:47 +0100, Pavel Stehule wrote: > The most significant issue was missing correct estimation for coalesce > function. > He had to rewrite coalesce(var, X) = X to "var IS NULL or var = X". > Then the result was very satisfactory. > > postgres=# explain analyze select * from xxx where coalesce(a, 0) = 0; > QUERY PLAN > > ---------------------------------------------------------------------------------------------------- > Seq Scan on xxx (cost=0.00..194.00 rows=60 width=4) (actual > time=0.041..4.276 rows=11000 loops=1)
I think that this is asking for a planner support function: https://www.postgresql.org/docs/current/xfunc-optimization.html Yours, Laurenz Albe
