Re: Do function calls the cached? - Mailing list pgsql-general

From David G. Johnston
Subject Re: Do function calls the cached?
Date
Msg-id CAKFQuwaaLDj7Rb1pVjHSdSaU6Q030zX6j1_g=VK-dNwDqXsArA@mail.gmail.com
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In response to Do function calls the cached?  (Daniel Caldeweyher <dcalde@gmail.com>)
Responses Re: Do function calls the cached?  (Daniel Caldeweyher <dcalde@gmail.com>)
List pgsql-general
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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