pgsql: Teach planner to short-circuit EXCEPT/INTERSECT with dummy input

Teach planner to short-circuit EXCEPT/INTERSECT with dummy inputs When either inputs of an INTERSECT [ALL] operator are proven not to return any results (a dummy rel), then mark the entire INTERSECT operation as dummy. Likewise, if an EXCEPT [ALL] operation's left input is proven empty, then mark

pgsql: Revert "Improve docs syntax checking"

Revert "Improve docs syntax checking" This reverts commit b292256272623d1a7532f3893a4565d1944742b4. Further discussion is needed Discussion: https://postgr.es/m/[email protected] Branch -- master Details --- https://git.postgresql.org/pg/commitdiff/5b