Re: Is postgres able to share sorts required by common partition window functions?

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От Sebastien Arod
Тема Re: Is postgres able to share sorts required by common partition window functions?
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Msg-id CADd42iFGCSuscEeW1yLULLMxq_sD8aVxn=gy+Z7xABC0YeXEDQ@mail.gmail.com
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Ответ на Re: Is postgres able to share sorts required by common partition window functions?  (Michael Lewis <mlewis@entrata.com>)
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Hi Michael,

I simplified the real query before posting it here and I now realize that I oversimplified things.

Unfortunately the real query cannot be re-written with a group by.

Some of the window functions are more complex with order by clause using complex expressions involving multiple columns.

The following example would be more realistic:

select distinct
  c1,
  first_value(c2) OVER (PARTITION BY c1 order by c2, c4) AS c2,
  first_value(c3) OVER (PARTITION BY c1 order by coalesce(c4, '000'), c3) AS c3
from  
  t;



On Mon, Jul 6, 2020 at 9:55 PM Michael Lewis <mlewis@entrata.com> wrote:
Does this give the same result and do the optimization you want?

select
  c1,
  min(c2) AS c2,
  min(c3) AS c3,
  min(c4) AS c4
from  
  t
group by
  c1;

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