Re: Combine function returning NULL unhandled?

On Mon, Nov 20, 2017 at 10:36 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> The plain transition case contains:
> if (pergroupstate->transValueIsNull)
> {
> /*
> * Don't call a strict function with NULL inputs. Note it is
> * possible to get here despite the above tests, if the transfn is
> * strict *and* returned a NULL on a prior cycle. If that happens
> * we will propagate the NULL all the way to the end.
> */
> return;
> }
>
> how come similar logic is not present for combine functions? I don't see
> any checks preventing a combinefunc from returning NULL, nor do I see
> https://www.postgresql.org/docs/devel/static/sql-createaggregate.html
> spell out a requirement that that not be the case.

I don't know of a reason why that logic shouldn't be present for the
combine-function case as well. It seems like it should be pretty
straightforward to write a test that hits that case and watch it blow
up ... assuming it does, then I guess we should back-patch the
addition of that logic.

--
Robert Haas
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