SQL

SQL Subquery and JOIN

SELECT DISTINCT Customers.customer_id, Customers.first_name
FROM Customers
INNER JOIN Orders
ON Customers.customer_id = Orders.customer_id
ORDER BY Customers.customer_id;

sql join on a subquery

SELECT * 
FROM
( SELECT ... FROM ... ) q1

INNER JOIN

( SELECT ... FROM ... ) q2

ON q1.colname = q2.colname