[alvherre]

Yes, MERGE is specified by the SQL standard. Our implementation (Postgres) aims to conform to the standard, so it should roughly match what both Oracle and SQL Server offer.

(Microsoft seems to have added a BY TARGET/BY SOURCE specification to the WHEN NOT MATCHED clause, which is not in the standard. Oracle seems to do DELETE in a different, nonstandard way.)

"Upsert" (which is called INSERT ON CONFLICT UPDATE in Postgres) is a different animal. It is not part of the SQL standard, which is why every database system does its own stuff.