Re: Soon-to-be-broken regression test case

Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> On 2018-Oct-11, Tom Lane wrote:
>> Hm, I'm not seeing any regression test result changes there.  However,
>> if you're just executing queries and not EXPLAIN'ing them, it's possible
>> something unwanted is happening under the hood.

> Hmm, no, the explains are there.  Here's one example -- maybe your new
> planner smarts do not change these plans for some reason

Oh, I see --- these are just "scalar-result sub-SELECTs", not
sub-select-in-FROM, so they never get into the join tree to begin with.
WHERE EXISTS is an exception because we attempt to translate it to a
JOIN_SEMI join, exposing an opportunity for subquery pullup.

            regards, tom lane