From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
---|---|
To: | Eske Rahn <eske(at)septima(dot)dk> |
Cc: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Björn Harrtell <bjorn(at)septima(dot)dk> |
Subject: | Re: Options to rowwise persist result of stable/immutable function with RECORD result |
Date: | 2023-03-22 23:46:09 |
Message-ID: | CAKFQuwb8YLvTZeq-ZGQKheEf2fD45CTt8dNHAf+_=oB7rqXD3A@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Wed, Mar 22, 2023 at 4:32 PM Eske Rahn <eske(at)septima(dot)dk> wrote:
> Hi,
>
> Thanks for the quick answer *:-D*
>
> That was a nice sideeffect of lateral.
>
> In the example, the calling code also gets simplified:
>
> WITH x AS (
> SELECT clock_timestamp() rowstart, *, clock_timestamp() rowend FROM (
> SELECT '1' inp UNION
> SELECT '2'
> ) y, LATERAL septima.foo(inp) g
> )
> SELECT * FROM x;
>
>
> That solved the issue at hand, in a much better way. Thanks
>
> Though I still fail to see *why* the other way should generally call the
> function for every column in the *result* record - if the function is
> STABLE or IMMUTABLE.
>
It gets rewritten to be effectively:
select func_call(...).col1, func_call(...).col2, func_call(...).col3
under the assumption that repeating the function call will be cheap and
side-effect free. It was never ideal but fixing that form of optimization
was harder than implementing LATERAL where the multi-column result has a
natural output in the form of a multi-column table. A normal function call
in the target list really means "return a single value" which is at odds
with writing .* after it.
David J.
From | Date | Subject | |
---|---|---|---|
Next Message | David G. Johnston | 2023-03-22 23:51:30 | Re: Options to rowwise persist result of stable/immutable function with RECORD result |
Previous Message | Eske Rahn | 2023-03-22 23:32:42 | Re: Options to rowwise persist result of stable/immutable function with RECORD result |