Hi hackers,
Currently, it is not possible for any fdw extension to support Merge
command, as that's prohibited in the parser.
In this proposal, we allow extensions to support Merge command via
`CustomScan` node by moving the Merge support check from parser to planner.
For existing fdw, they don't have to change anything. I changed
postgres_fdw mostly for documentation purposes.
See the attached patch.
Thanks,
Onder KALACI