Re: A new strategy for pull-up correlated ANY_SUBLINK

>
> It seems to me that the expressions "=" and "IN" are equivalent here due
> to the fact that the aggregated subquery returns only one value, and the
> result with the "IN" operation can be considered as the intersection of
> elements on the left and right. In this query, we have some kind of set on
> the left, among which there will be found or not only one element on the
> right.
>

Yes, they are equivalent at the final result, but there are some
differences at the execution level. the '=' case will be transformed
to a Subplan whose subPlanType is EXPR_SUBLINK, so if there
is more than 1 rows is returned in the subplan, error will be raised.

select * from tenk1 where
ten = (select ten from tenk1 i where i.two = tenk1.two );

ERROR: more than one row returned by a subquery used as an expression

However the IN case would not.
select * from tenk1 where
ten = (select ten from tenk1 i where i.two = tenk1.two ) is OK.

I think the test case you added is not related to this feature. the
difference is there even without the patch. so I kept the code
you changed, but not for the test case.

I took the liberty of adding this to your patch and added myself as
>> reviewer, if you don't mind.
>>
> Sure, the patch after your modification looks better than the original.
> I'm not sure how the test case around "because of got one row" is
> relevant to the current changes. After we reach to some agreement
> on the above discussion, I think v4 is good for committer to review!
>
>
> Thank you!) I am ready to discuss it.
>

Actually I meant to discuss the "Unfortunately, I found a request..", looks
we have reached an agreement there:)

--
Best Regards
Andy Fan