Re: Postgres_fdw join pushdown - wrong results with whole-row reference

On Wed, Jun 22, 2016 at 4:11 AM, Amit Langote
<Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> In an outer join we have to differentiate between a row being null (because
>> there was no joining row on nullable side) and a non-null row with all
>> column values being null. If we cast the whole-row expression to a text
>> e.g. r.*::text and test the resultant value for nullness, it gives us what
>> we want. A null row casted to text is null and a row with all null values
>> casted to text is not null.
>
> You are right. There may be non-null rows with all columns null which are
> handled wrongly (as Rushabh reports) and the hack I proposed is not right
> for. Especially if from non-nullable side as in the reported case, NULL
> test for such a whole-row-var would produce the wrong result. Casting to
> text as your patch does produces the correct behavior.

I agree, but I think we'd better cast to pg_catalog.text instead, just
to be safe. Committed that way.

--
Robert Haas
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