How to have multiple colums in a variable/array - sql

Question

I have this query
select expiration_date, driver_id from all_requirements_driver_documents where expiration_date <= (now() + interval '1 month')::DATE and expiration_date > (now() - interval '7 day')::DATE
union
select expiration_date, driver_id from all_requirements_vehicle_documents where expiration_date <= (now() + interval '1 month')::DATE and expiration_date > (now() - interval '7 day')::DATE
I want to insert it into a variable in which I can loop and perform actions.
i.e unsatified_documents driver_expiring_documents;
where
create table if not exists driver_expiring_documents (
driver_id text,
expiration_date date
);
and then loop through it
if(unsatified_documents != '{}') then
foreach expiring_doc in array unsatified_documents loop
-- -- Get Driver ID --
driver_id_arg := expiring_doc.driver_id;
expiring_date := expiring_doc.expiration_date;
end loop;
end if;
How can I do it?

Answer 1

You can store it in an array variable, but if you want to loop through the results, that would be unnecessarily complicated and inefficient. You'd have to pack it into a data structure that potentially uses a lot of RAM, only to unpack it right away.
Simply do
DECLARE
r record;
BEGIN
FOR r IN
select expiration_date, driver_id from ... WHERE ...
union
select expiration_date, driver_id from ... where ...
LOOP
/* do something with "r.expiration_date" and "r.driver_id" */
END LOOP;
END;

Answer 2

You can use a custom type, for example:
CREATE TYPE my_doc
AS
(
driver_id text,
expiration_date date
);
Then, if you want make an array of these values you can do:
SELECT array_agg((driver_id, expiration_date)::my_doc)
FROM driver_expiring_documents;
But you don't even need the array, which can be pretty big, you can just loop in a function with this simple query:
SELECT (driver_id, expiration_date)::my_doc
FROM driver_expiring_documents;
Or, you can skip the intermediate table and select with the union:
select (expiration_date, driver_id)::my_doc from all_requirements_driver_documents where expiration_date <= (now() + interval '1 month')::DATE and expiration_date > (now() - interval '7 day')::DATE
union
select (expiration_date, driver_id)::my_doc from all_requirements_vehicle_documents where expiration_date <= (now() + interval '1 month')::DATE and expiration_date > (now() - interval '7 day')::DATE
And just a consideration: if you can, use UNION ALL, it will be faster.