Thread: using a selected row as a function parameter

Hi all,

I've been struggling with this for a while and haven't found anything
on the 'Net about it.  I've created a function that takes two table
rows as a parameters.  I'd like to use the output of a select (two
single rows) as the parameters, but I can't get it to work.  What am I
missing?

The function prototype looks like this:

CREATE OR REPLACE FUNCTION queue.apply_routing_rule(                      queue.messages,
queue.routing_rules                     ) RETURNS int2 

and I would like to call it like this:

SELECT queue.apply_routing_rule(                      (SELECT * from queue.messages WHERE id = 1),
(SELECT* from queue.routing_rules WHERE id = 1)                     ); 

I get an error message along the lines of "sub-query must return a
single value".  I've tried different combinations of "CAST" and "ROW"
functions, but they give syntax errors.

Any suggestions?

Regards,
Ami.

Ami Ganguli <ami.ganguli@gmail.com> writes:
> SELECT queue.apply_routing_rule( 
>                       (SELECT * from queue.messages WHERE id = 1),
>                       (SELECT * from queue.routing_rules WHERE id = 1)
>                       );

Not sure if that particular syntax should be expected to work,
but why not

SELECT queue.apply_routing_rule(messages.*, routing_rules.*)
FROM queue.messages, queue.routing_rules
WHERE messages.id = 1 AND routing_rules.id = 1;

The query as you want to write it will certainly fail anyway if there's
more than one row with id = 1 in either table, so it's not like there's
some huge inefficiency in doing it as a join.
        regards, tom lane

On Fri, Jun 03, 2005 at 05:44:59PM +0300, Ami Ganguli wrote:
>
> SELECT queue.apply_routing_rule( 
>                       (SELECT * from queue.messages WHERE id = 1),
>                       (SELECT * from queue.routing_rules WHERE id = 1)
>                       );
> 
> I get an error message along the lines of "sub-query must return a
> single value".

The error I get is "subquery must return only one column".  Queries
like the following should work in 8.0.x:

SELECT queue.apply_routing_rule(m, r)
FROM (SELECT * FROM queue.messages WHERE id = 1) AS m,    (SELECT * FROM queue.routing_rules WHERE id = 1) AS r;

SELECT queue.apply_routing_rule(m, r)
FROM queue.messages AS m,     queue.routing_rules AS r
WHERE m.id = 1  AND r.id = 1;

-- 
Michael Fuhr
http://www.fuhr.org/~mfuhr/