Re: MERGE bug report

On 2022-Apr-11, Richard Guo wrote:

> At first I was wondering whether we need to also include vars used in
> each action's targetlist, just as what we did for each action's qual.
> Then later I realized parse_merge.c already did that. But now it looks
> much better to process them two in preprocess_targetlist.

Yeah. I pushed that.

However, now EXPLAIN VERBOSE doesn't show the columns from the source
relation in the Output line --- I think only those that are used as join
quals are shown, thanks to distribute_quals_to_rels. I think it would
be better to fix this. Maybe expanding the source target list earlier
is called for, after all. I looked at transformUpdateStmt and siblings
for inspiration, but came out blank.

> A minor comment is that we can use list_concat_copy(list1, list2)
> instead of list_concat(list_copy(list1), list2) for better efficiency.

Thanks for that tip.

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