Thread: How to access multicolumn function results?

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.

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