How to return a result set from a Postgresql function while inserting rows inside a loop? - postgresql

Question

I'm trying to dynamically generate text values, insert them into a table while checking their uniqueness, and return such values from a function. I managed to do #1 and #2, but I can't find a way for the function to return the generated values. The last try is this one. Returning a table from the function and creating a temp table in the body of the function that's used in the Return clause.
CREATE OR REPLACE FUNCTION add_unique_codes(
number_of_codes_to_generate integer,
code_length integer,
effective_date date,
expiry_date date)
RETURNS TABLE(generated_code text)
LANGUAGE 'plpgsql'
AS $BODY$
DECLARE
random_code text := '';
BEGIN
CREATE TEMPORARY TABLE generated_codes(cd text) ON COMMIT DROP;
FOR i IN 1..number_of_codes_to_generate LOOP
random_code = unique_random_code(code_length, 'p_codes', 'id');
INSERT INTO p_codes (code, type, effective_date, expiry_date)
VALUES (random_code, 'B', effective_date, expiry_date);
INSERT INTO generated_codes VALUES (random_code);
END LOOP;
RETURN QUERY SELECT cd FROM generated_codes;
END;
$BODY$;
As I said, the function unique_random_code is working fine and I also see the new "codes" inserted in the p_codes table. The only issue is the function doesn't return the set of "codes" back.
Thank you

Answer 1

No need for a temporary table or a slow PL/pgSQL FOR loop. You can use generate_series() to generate the number of rows, and the returning option of the INSERT statement to return those rows:
CREATE OR REPLACE FUNCTION add_unique_codes(
number_of_codes_to_generate integer,
code_length integer,
effective_date date,
expiry_date date)
RETURNS TABLE(generated_code text)
LANGUAGE sql
AS
$BODY$
INSERT INTO p_codes (code, type, effective_date, expiry_date)
select unique_random_code(code_length, 'p_codes', 'id'), 'B', effective_date, expiry_date
from generate_series(1, number_of_codes_to_generate)
returning code;
$BODY$;