Re: [HACKERS] MERGE SQL Statement for PG11

The question I have is, if the USING qual evaluates to false or NULL, should we silently ignore the tuple (like regular UPDATE does) or throw an error (like INSERT ON CONFLICT DO UPDATE)? ISTM that we might have decided to throw an error in case of INSERT ON CONFLICT to avoid any confusion where the tuple is neither inserted nor updated. Similar situation may arise with MERGE because for a source row, we may neither do UPDATE (because of RLS) nor INSERT because a matching tuple already exists. But someone may argue that we should stay closer to regular UPDATE/DELETE. Apart from that, are there any security angles that we need to be mindful of and would those impact the choice?

SELECT policies will be applied to the target table during the scan and rows which do not pass SELECT quals will not be processed at all. If there are NOT MATCHED actions, we might end up inserting duplicate rows in that case or throw errors, but I don't see anything wrong with that. Similar things would have happened if someone tried to insert rows into the table using regular INSERT.

Similarly, INSERT policies will be applied when MERGE attempts to INSERT a row into the table and error will be thrown if the row does not satisfy INSERT policies.

Thanks,

Pavan