Recursive pl/pgsql function ...

'k, this isn't quite working as expected (or, rather, hoped) ... I've created a
recursive function (that does work nicely) that takes a date in the past, and
keeps advancing in steps of 'n months' until the date is in the future:

CREATE OR REPLACE FUNCTION get_next_billing_date(timestamp with time zone,
int4) RETURNS TIMESTAMP AS '
DECLARE
max_date RECORD;
ret TIMESTAMP WITH TIME ZONE;

start_date ALIAS FOR $1;
payment_period ALIAS FOR $2;

BEGIN

SELECT INTO max_date CASE WHEN now() < start_date + ( payment_period || ''
months'')::interval THEN payment_period ELSE NULL END;

IF max_date.case IS NULL THEN
SELECT INTO ret get_next_billing_date(start_date + ( payment_period || ''
months'')::interval, payment_period);
ELSE
RETURN start_date + ( payment_period || '' months'')::interval;
END IF;
RETURN ret;
END;
' LANGUAGE plpgsql;

It works, no problem there:

# select get_next_billing_date('2005-10-15', 3);
get_next_billing_date
-----------------------
2007-01-15 00:00:00
(1 row)

But, as soon as I try and use that function as a field in a query, it gives an
error:

1 Record:
# select get_next_billing_date(activated, 12) from company_details where
company_id = 771;
get_next_billing_date
----------------------------
2007-05-03 15:09:19.491958
(1 row)

More then one Record:
# select get_next_billing_date(activated, 12) from company_details;
ERROR: control reached end of function without RETURN
CONTEXT: PL/pgSQL function "get_next_billing_date"

Something I've written wrong in the function, or just not something that is
doable?

Thanks ...

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