Question

I’m learning how to write functions in Postgresql. I’ve defined a function called _tmp_myfunction() which takes in an id and returns a table (I also define a table object type called _tmp_mytable)

-- create object type to be returned
CREATE TYPE _tmp_mytable AS (
    id      integer, 
    cost    double precision
    );

-- create function which returns query
CREATE OR REPLACE FUNCTION _tmp_myfunction(
    id    integer
    )
RETURNS SETOF _tmp_mytable AS $$
BEGIN  
  RETURN QUERY 
  SELECT
    sales.gid,
    cost  
  FROM 
    sales
  WHERE
    id = sales.gid;
  END;
$$ LANGUAGE plpgsql;

This works fine when I use one id and call it using the following approach:

SELECT * FROM _tmp_myfunction(402);

What I would like to be able to do is to call it, but to use a column of values instead of just one value. However, if I use the following approach I end up with all values of the table in one column, separated by commas:

-- call function using all values in a column
SELECT _tmp_myfunction(t.id)
FROM transactions as t;

I understand that I can get the same result if I use SELECT _tmp_myfunction(402); instead of SELECT * FROM _tmp_myfunction(402); but I don’t know how to construct my function in such a way that I do not get composite values when I pass in a column of values.

Answer 1

You can write something like that:

SELECT (t2.function_row).id,
       (t2.function_row).cost
FROM (SELECT _tmp_myfunction(t.id) as function_row
     FROM transactions  t ) t2;

It will give you the fields, instead of composite rows.