Tom Lane wrote: > "=?ISO-8859-1?B?QXJtb3I=?=" <yupengst...@qq.com> writes: > > Because PG does not pushdown qual to the none of the subquery. And I > > check the source code, find some comments in > > src/backend/optimizer/path/allpaths.c, which says "If the subquery > > contains EXCEPT or EXCEPT ALL set ops we cannot push quals into it, because > > that could change the results". > > However, for this case, I think we can pushdown qual to the left most > > subquery of EXCEPT, just like other database does. > > That is not an adequate argument for such a change being okay. Postgres, > with its extensible set of datatypes, has to be much more careful about > the semantic soundness of optimizations than some other DBs do.
Can we use the record_image_ops mechanism here? -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
