Table schema:
CREATE TABLE customer_orders (order_id VARCHAR, order_date INTEGER); CREATE TABLE order_items (order_quantity INTEGER, order_id VARCHAR)

Question: Find the total amount of products ordered before 2018-03-17 07:13:53.
SQL: SELECT SUM(t2.order_quantity) FROM customer_orders AS t1 JOIN order_items AS t2 ON t1.order_id = t2.order_id WHERE t1.order_date < "2018-03-17 07:13:53"