Querying relational databases Subqueries

I am kind of stuck on the querying relational databases course by Andrew Chalkey..

I have produced the following for on of the questions but not sure if its correct or wether there is a better way, I am sure there is lol:

Here is my attempt:

   -- Generate a report that lists a patron's first name, email and loan count for loans that haven't been returned
SELECT first_name, email, id, COUNT(id) AS "Loan Count" FROM patrons AS p
  INNER JOIN (SELECT loans_south.patron_id FROM loans_south WHERE returned_on IS NULL) AS t
  ON t.patron_id = p.id
  GROUP BY t.patron_id
    UNION
  SELECT first_name, email, id, COUNT(id) AS "Loan Count" FROM patrons AS pat
  INNER JOIN (SELECT loans_north.patron_id FROM loans_north WHERE returned_on IS NULL) AS tem
  ON tem.patron_id = pat.id
  GROUP BY tem.patron_id
  ORDER BY "Loan Count" DESC;

The second query after the union is just a copy of the one above but searching through the second table called loans_north I wish i could just get it to look through the one joined table..

I also wonder if in a sub query where you put the query in brackets if you can do something

like (SELECT name from table_one UNION SELECT name from table_two) this would hopefully union two tables and this could be the derived table...

Can you store results from queries in variables.. and then pass them to other queries ?