| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Jeevan Chalke <jeevan(dot)chalke(at)enterprisedb(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
| Subject: | Re: Soon-to-be-broken regression test case |
| Date: | 2018-10-11 17:19:11 |
| Message-ID: | 8265.1539278351@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)2ndquadrant(dot)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
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