Using PLPGSQL function result in a join query - postgresql

Question

I am developing an application its database is Postgres 9.5
I am having the following plpgsql function
CREATE OR REPLACE FUNCTION public.getall_available_products(
IN start_day_id integer,
IN end_day_id integer)
RETURNS TABLE(id integer) AS
$BODY$
SELECT product_id As id
FROM product_days
WHERE available > 0
AND days_id BETWEEN start_day_id AND end_day_id
$BODY$
LANGUAGE sql VOLATILE
I need to use the result of the above function in a join query in another plpgsql
function
CREATE OR REPLACE FUNCTION public.get_available_product_details(
IN start_day_id integer,
IN end_day_id integer)
RETURNS SETOF record AS
$BODY$declare
begin
SELECT pd.days_id As pd_days_id, pd.id AS p_id, pd.name AS p_name
FROM product p JOIN product_days pd
Using(id)
WHERE pd.id in
Select * from
//here I need to use the result of the getall_available_products
//function
end;
$BODY$
LANGUAGE plpgsql VOLATILE
How should I use the result of the first function in the second function? where I specify with comments.

Answer 1

You can select from set / table returning functions like tables or views. In your case:
SELECT pd.days_id As pd_days_id, pd.id AS p_id, pd.name AS p_name
FROM product p JOIN product_days pd USING(id)
WHERE pd.id IN
(SELECT a.id FROM public.getall_available_products(start_day_id, end_day_id) a);
You may even join with functions:
SELECT pd.days_id As pd_days_id, pd.id AS p_id, pd.name AS p_name
FROM product p JOIN product_days pd USING(id)
JOIN public.getall_available_products(start_day_id, end_day_id) a ON pd.id = a.id;
This should give the same result.
Note: If you want pass column values as function arguments you should take a look at the relatively new keyword LATERAL.