Re: Supporting MERGE on updatable views

On Tue, 30 Jan 2024 at 11:58, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> This looks quite nice, thanks.  LGTM.
>

Going over this again, I spotted a bug -- the UPDATE path in
ExecMergeMatched() wasn't calling ExecUpdateEpilogue() for
trigger-updatable views, because it wasn't setting updateCxt.updated
to true. (This matters if you have an auto-updatable view WITH CHECK
OPTION on top of a trigger-updatable view, so I've added a new test
there.)

Rather than setting updateCxt.updated to true, making the
trigger-invoking code in ExecMergeMatched() diverge from ExecUpdate(),
a better fix is to simply remove the UpdateContext.updated flag
entirely. The only place that reads it is this code in
ExecMergeMatched():

    if (result == TM_Ok && updateCxt.updated)
    {
        ExecUpdateEpilogue(context, &updateCxt, resultRelInfo,
                           tupleid, NULL, newslot);

where result is the result from ExecUpdateAct(). However, all paths
through ExecUpdateAct() that return TM_Ok also set updateCxt.updated
to true, so the flag is redundant. It looks like that has always been
the case, ever since it was introduced. Getting rid of it is a useful
simplification, and brings the UPDATE path in ExecMergeMatched() more
into line with ExecUpdate(), which always calls ExecUpdateEpilogue()
if ExecUpdateAct() returns TM_Ok.

Aside from that, I've done a little more copy-editing and added a few
more test cases, and I think this is pretty-much good to go, though I
think I'll split this up into separate commits, since removing
UpdateContext.updated isn't really related to the MERGE INTO view
feature.

Regards,
Dean