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Re: Is "DISTINCT" making a diffence in: SELECT [DISTINCT] ... EXCEPT - Mailing list pgsql-general

From Erik Wienhold
Subject Re: Is "DISTINCT" making a diffence in: SELECT [DISTINCT] ... EXCEPT
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Msg-id p7bccg4lc6o6hehaujpmauh3mymdor33exspwjwq4s4w3sud4m@zwry4unn65wp
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In response to Is "DISTINCT" making a diffence in: SELECT [DISTINCT] ... EXCEPT  (Dimitrios Apostolou <jimis@gmx.net>)
Responses Re: Is "DISTINCT" making a diffence in: SELECT [DISTINCT] ... EXCEPT
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On 2023-11-15 10:57 +0100, Dimitrios Apostolou wrote:
> SELECT [DISTINCT] ... EXCEPT ...
> 
> In this query I get the same results regardless of including DISTINCT or
> not. But I get different query plans, I get an extra HashAggregate node
> in the case of SELECT DISTINCT. Any idea why?

As Tom Lane recently wrote[1] EXCEPT is not optimized and will operate
on the subqueries which are planned independently.

[1] https://www.postgresql.org/message-id/2664450.1698799927@sss.pgh.pa.us

-- 
Erik

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