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

I wonder whether such a whole-row-var would arise from the nullable side
> of a join? I guess not. Not that I'm saying we shouldn't account for that
> case at all since any and every whole-row-var in the targetlist currently
> gets that treatment, even those that are known non-nullable. Couldn't we
> have prevented the latter somehow? IOW, only generate the CASE WHEN when
> a Var being deparsed is known nullable as the comment there says:
>
> deparse.c:
>
> 1639 /*
> 1640 * In case the whole-row reference is under an outer join then it has
> 1641 * to go NULL whenver the rest of the row goes NULL. Deparsing a join
> 1642 * query would always involve multiple relations, thus qualify_col
> 1643 * would be true.
> 1644 */
> 1645 if (qualify_col)
> 1646 {
> 1647 appendStringInfoString(buf, "CASE WHEN");
> 1648 ADD_REL_QUALIFIER(buf, varno);
> 1649 appendStringInfo(buf, "* IS NOT NULL THEN ");
> 1650 }
>
> But I guess just fixing the expression as your patch does may be just fine.
>
>
I thought about that, but it means that we have compute the nullable relids
(which isn't a big deal I guess). That's something more than necessary for
fixing the bug, which is the focus in beta stage right now.

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company