Re: MERGE ... WHEN NOT MATCHED BY SOURCE

On Thu, 5 Jan 2023 at 13:21, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> wrote:
>
> On Thu, 5 Jan 2023 at 11:03, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> >
> > > + /* Join type required */
> > > + if (left_join && right_join)
> > > + qry->mergeJoinType = JOIN_FULL;
> > > + else if (left_join)
> > > + qry->mergeJoinType = JOIN_LEFT;
> > > + else if (right_join)
> > > + qry->mergeJoinType = JOIN_RIGHT;
> > > + else
> > > + qry->mergeJoinType = JOIN_INNER;
> >
> > One of the review comments that MERGE got initially was that parse
> > analysis was not a place to "do query optimization", in the sense that
> > the original code was making a decision whether to make an outer or
> > inner join based on the set of WHEN clauses that appear in the command.
> > That's how we ended up with transform_MERGE_to_join and
> > mergeUseOuterJoin instead. This new code is certainly not the same, but
> > it makes me a bit unconfortable. Maybe it's OK, though.
> >
>
> Yeah I agree, it's a bit ugly. Perhaps a better solution would be to
> do away with that field entirely and just make the decision in
> transform_MERGE_to_join() by examining the action list again.
>

Attached is an updated patch taking that approach, allowing
mergeUseOuterJoin to be removed from the Query node, which I think is
probably a good thing.

Aside from that, it includes a few additional comment updates in the
executor that I'd missed, and psql tab completion support.

Regards,
Dean