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ExecMakeTableFunctionResult(), which is used in SELECT FROM function(...) cases, formerly treated a simple NULL output from a function that both returnsSet and returnsTuple as a violation of the SRF protocol. What seems better is to treat a NULL output as equivalent to ROW(NULL,NULL,...). Without this, cases such as SELECT FROM unnest(...) on an array of composite are vulnerable to unexpected and not-very-helpful failures. Old code comments here suggested an alternative of just ignoring simple-NULL outputs, but that doesn't seem very principled. This change had been hung up for a long time due to uncertainty about how much we wanted to buy into the equivalence of simple NULL and ROW(NULL,NULL,...). I think that's been mostly resolved by the discussion around bug #14235, so let's go ahead and do it. Per bug #7808 from Joe Van Dyk. Although this is a pretty old report, fixing it smells a bit more like a new feature than a bug fix, and the lack of other similar complaints suggests that we shouldn't take much risk of destabilization by back-patching. (Maybe that could be revisited once this patch has withstood some field usage.) Andrew Gierth and Tom Lane Report: <E1TurJE-0006Es-TK@wrigleys.postgresql.org>
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