Returning a table from a cursor - postgresql

Question

I have a function that returns a table of calculated values based on a customer id. I need to get values for all customers; I made a cursor but I can't make it return the set.
Customer table:
id name
---- ----
CN102 Dude
CN103 Guy
CN104 Mate
Function:
SELECT * FROM get_custom_fields('CN104');
name field_value
---- -----
POP 9
Z44 blue
POP 19
Please note there could be multiple rows with the same name.
This is my cursor:
CREATE OR REPLACE FUNCTION my_cursor ()
RETURNS SETOF RECORD AS $$
DECLARE
v_customer_rec RECORD;
v_pop RECORD;
BEGIN
FOR v_customer_rec IN SELECT ucn FROM customer LOOP
SELECT INTO v_pop field_value from get_custom_fields(v_customer_rec.ucn) where custom_field='POP';
RAISE NOTICE 'Customer % Value %', v_customer_rec.ucn,v_pop;
-- RETURN QUERY select field_value from get_custom_fields(v_customer_rec.ucn) where custom_field='POP';
END LOOP;
RETURN;
END;
$$ LANGUAGE plpgsql;
This returns:
db=# select my_cursor();
NOTICE: Customer CN102 Value (5)
NOTICE: Customer CN103 Value (12)
NOTICE: Customer CN104 Value (9)
NOTICE: Customer CN104 Value (19)
my_cursor
-------------
(0 rows)
So I know it should work. But if use RETURN QUERY (as commented in the code) I get the following error:
ERROR: set-valued function called in context that cannot accept a set
CONTEXT: PL/pgSQL function "my_cursor" line 9 at RETURN QUERY
How can I make it return the values in a table or set?
I'm trying to get:
ucn field_value
----- -----------
CN102 5
CN103 12
CN104 9
CN104 19

Answer 1

Your (simplified) function could look like this:
CREATE OR REPLACE FUNCTION my_cursor()
RETURNS SETOF RECORD AS
$func$
DECLARE
_ucn text;
BEGIN
FOR _ucn IN
SELECT ucn FROM customer
LOOP
RETURN QUERY
SELECT *
FROM get_custom_fields(_ucn)
WHERE name = 'POP';
END LOOP;
RETURN;
END
$func$ LANGUAGE plpgsql;
I am assuming data type text for ucn here.
But really, you should define the RETURN type, to avoid having to provide a column definition list with every call. If you just want the column field_value, and it is type text:
CREATE OR REPLACE FUNCTION my_cursor()
RETURNS SETOF text AS
$func$
DECLARE
_ucn text;
BEGIN
FOR _ucn IN
SELECT ucn FROM customer
LOOP
RETURN QUERY
SELECT field_value
FROM get_custom_fields(_ucn)
WHERE name = 'POP';
END LOOP;
RETURN;
END
$func$ LANGUAGE plpgsql;
Or use RETURNS TABLE() for multiple columns per row:
CREATE OR REPLACE FUNCTION my_cursor()
RETURNS TABLE(ucn text, field_value text) AS
$func$
DECLARE
_ucn text;
BEGIN
FOR _ucn IN
SELECT c.ucn FROM customer c
LOOP
RETURN QUERY
SELECT g.ucn, g.field_value
FROM get_custom_fields(_ucn) g
WHERE g.name = 'POP';
END LOOP;
RETURN;
END
$func$ LANGUAGE plpgsql;
Be aware that the columns of the RETURN type are visible in the function body. Table-qualify columns of the same name to avoid naming conflicts.