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* How to access multicolumn function results?
@ 2013-01-24 00:58 Andreas <maps.on@gmx.net>
2013-01-24 01:42 ` Re: How to access multicolumn function results? Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 1 reply; 2+ messages in thread
From: Andreas @ 2013-01-24 00:58 UTC (permalink / raw)
To: pgsql-sql
Hi
I've got functions that return a TABLE.
If I call it with constant parameters like:
SELECT * FROM some_fct( 42 );
I get a table with column names as the result as intended.
When I rather call it with the parameter coming from another table I get
a set of records where I don't know how to access specific columns:
SELECT some_fct( some_id ) FROM some_other_table;
Now I get e.g. the result
( id1, value11, value12, value13 ),
( id1, value14, value15, value16 ),
( id2, value24, value25, value26 ),
...
How can I split this up to look like a normal table or view with the
column names that are defined in the RETURNS TABLE ( ... ) expression of
the function.
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^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: How to access multicolumn function results?
2013-01-24 00:58 How to access multicolumn function results? Andreas <maps.on@gmx.net>
@ 2013-01-24 01:42 ` Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 0 replies; 2+ messages in thread
From: Tom Lane @ 2013-01-24 01:42 UTC (permalink / raw)
To: Andreas <maps.on@gmx.net>; +Cc: pgsql-sql
Andreas <maps.on@gmx.net> writes:
> SELECT some_fct( some_id ) FROM some_other_table;
> How can I split this up to look like a normal table or view with the
> column names that are defined in the RETURNS TABLE ( ... ) expression of
> the function.
The easy way is
SELECT (some_fct(some_id)).* FROM some_other_table;
If you're not too concerned about efficiency, you're done. However this
isn't very efficient, because the way the parser deals with expanding
the "*" is to make N copies of the function call, as you can see with
EXPLAIN VERBOSE --- you'll see something similar to
Output: (some_fct(some_id)).fld1, (some_fct(some_id)).fld2, ...
If the function is expensive enough that that's a problem, the basic
way to fix it is
SELECT (ss.x).* FROM
(SELECT some_fct(some_id) AS x FROM some_other_table) ss;
With a RETURNS TABLE function, this should be good enough. With simpler
functions you might have to insert OFFSET 0 into the sub-select to keep
the planner from "flattening" it into the upper query and producing the
same multiple-evaluation situation.
regards, tom lane
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2013-01-24 00:58 How to access multicolumn function results? Andreas <maps.on@gmx.net>
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