Re: MERGE issues around inheritance

Álvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> 于2025年5月24日周六 17:11写道：

> On 2025-May-21, Andres Freund wrote:
>
> > Hi,
> >
> > In [1] I added some verification to projection building, to check if the
> > tupleslot passed to ExecBuildProjectionInfo() is compatible with the
> target
> > list. One query in merge.sql [2] got flagged.
> >
> > Trying to debug that issue, I found another problem. This leaves us with:
> >
> > 1) w/ inheritance INSERTed rows are not returned by RETURNING. This
> seems to
> > just generally not work with MERGE
>
> Hmm, curious. One thing to observe is that the original source tuple is
> in the child table, but the tuple inserted by MERGE ends up in the
> parent table. I'm guessing that the code gets confused as to the
> relation that the tuple in the returned slot comes from, and that
> somehow makes it somehow not "see" the tuple to process for RETURNING?
> I dunno. CC'ing Dean, who is more familiar with this code than I am.
>

In ExecMergeNotMatched(), we passed the mtstate->rootResultRelInfo to
ExecInsert().
In this case, the ri_projectReturning of mtstate->rootResultRelInfo is
NULL, in ExecInsert(),
the "if (resultRelInfo->ri_projectReturning)" branch will not run, so
inheritance INSERTed rows are not returned by RETURNING.

The mtstate->rootResultRelInfo assigned in ExecInitModifyTable() is only
here:
if (node->rootRelation > 0)
{
Assert(bms_is_member(node->rootRelation, estate->es_unpruned_relids));
mtstate->rootResultRelInfo = makeNode(ResultRelInfo);
ExecInitResultRelation(estate, mtstate->rootResultRelInfo,
node->rootRelation);
}
The ri_projectReturning is not assigned.

I try to pass resultRelInfo to ExecInsert, the inherited INSERTed rows are
returned by RETURNING.
But some test cases in regression failed.

--
Thanks,
Tender Wang