#3962

Thank you for your contribution!

Unfortunately, it is too intrusive and contains random unrelated changes, including features, that we don't want to support on our side, such as non-standard operators. They create a lot of unnecessary complexity. H2 is not an emulator of other database systems and cannot have all their crazy features.

Actually it will be much better to write and contribute an implementation of standard data change delta tables to PostgreSQL. They are more powerful than RETURING from PostgreSQL.

If you can't do it for some reason, please implement only one feature per pull request and discuss what you add with community before writing an actual implementation.

For RETURNING clause it will be better to translate this syntax to SELECT … FROM FINAL TABLE (…) in the parser instead of messing with various parts of H2. You don't need to generate a new SQL here, you can simply construct a org.h2.command.query.Select with these expressions and a org.h2.table.DataChangeDeltaTable with original DML command. It should be relatively simple and it will not disturb code base of H2 too much for this compatibility-only feature. Of course, it must be restricted to PostgreSQL compatibility mode.