Re: NOT IN subquery optimization - Mailing list pgsql-hackers

From Andres Freund
Subject Re: NOT IN subquery optimization
Date
Msg-id D3BABCAC-875D-40C8-B020-4FD4B274738A@anarazel.de
Whole thread Raw
In response to Re: NOT IN subquery optimization  (David Rowley <david.rowley@2ndquadrant.com>)
Responses Re: NOT IN subquery optimization
List pgsql-hackers
Hi,

On March 1, 2019 4:53:03 AM PST, David Rowley <david.rowley@2ndquadrant.com> wrote:
>On Fri, 1 Mar 2019 at 15:27, Richard Guo <riguo@pivotal.io> wrote:
>> I have reviewed your patch. Good job except two issues I can find:
>>
>> 1. The patch would give wrong results when the inner side is empty.
>In this
>> case, the whole data from outer side should be in the outputs. But
>with the
>> patch, we will lose the NULLs from outer side.
>>
>> 2. Because of the new added predicate 'OR (var is NULL)', we cannot
>use hash
>> join or merge join to do the ANTI JOIN.  Nested loop becomes the only
>choice,
>> which is low-efficency.
>
>Yeah. Both of these seem pretty fundamental, so setting the patch to
>waiting on author.

I've not checked, but could we please make sure these cases are covered in the regression tests today with a single
liner?Seems people had to rediscover them a number of times now, and unless this thread results in an integrated
featuresoonish, it seems likely other people will again. 

Andres
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.


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