Re: stable and immutable functions in GROUP BY clauses. - Mailing list pgsql-performance

From Marc Mamin
Subject Re: stable and immutable functions in GROUP BY clauses.
Date
Msg-id B6F6FD62F2624C4C9916AC0175D56D880CE1B381@jenmbs01.ad.intershop.net
Whole thread Raw
In response to stable and immutable functions in GROUP BY clauses.  (Marc Mamin <M.Mamin@intershop.de>)
List pgsql-performance
>
> Hello,
>
> Stable and immutable functions do not improve performance when used within the GROUP BY clause.
> Here, the function will be called for each row.
>
> To avoid it, I can replace the funtion by its arguments within GROUP BY.

Shame on me !
This is of course bullsh...  It has nothing to do with immutability and can only applies to few cases

e.g: it's fine for select x+1 ... group by  x,
but not for        select x^2 ... group by  x

Marc Mamin


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