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
0001-Allow-FDW-extensions-to-support-MERGE-command-via-Cu.patch
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