Re: Do function calls the cached?

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От Daniel Caldeweyher
Тема Re: Do function calls the cached?
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Msg-id CADVnD3BPmVSkTGKQHE4Ssahdjw8-HmiGP7YR-vVC0sAZfU4oNg@mail.gmail.com
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Ответ на Re: Do function calls the cached?  ("David G. Johnston" <david.g.johnston@gmail.com>)
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Thanks David,

Lateral did the trick:

CREATE VIEW with_keywords AS
SELECT x,y,z, keywords.a, keywords.b, keywords.c
FROM large_table l, LATERAL extract_keywords(l.*) keywords(a,b,c)

Regards,
Daniel

On Wed, Aug 31, 2016 at 6:46 AM, David G. Johnston <david.g.johnston@gmail.com> wrote:
On Tue, Aug 30, 2016 at 4:15 PM, Daniel Caldeweyher <dcalde@gmail.com> wrote:

select x,y,z, (extract_keywords(l.*)).*

​[...]​
 
Does this mean the function gets called three time?

​Yes.
​
 
(​function_call(...)).*​
 
​syntax is problematic.  You should avoid it via one of two options.

LATERAL (new way, preferred)
or
CTE​ (old way)

In the CTE version you make the call in the CTE but do "(col).*" in the main query.  This way the function is only called once to generate a composite output, then the composite output is exploded.

With LATERAL the system is smart enough to do it the right way.

David J.

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