Task: Text to Code
Input (English): Step 1: For each row in Customer_Orders table, find corresponding rows in Customers table and in Order_Items table.
Step 2: find the summation of order_quantity in the results of step 1 whose date_became_customer less than 2018-03-17 07:13:53
Output (English): SELECT Sum ( T3.order_quantity ) FROM Customers AS T1 JOIN Customer_Orders AS T2 ON T1.customer_id = T2.customer_id JOIN Order_Items AS T3 ON T2.order_id = T3.order_id WHERE T1.date_became_customer < "2018-03-17 07:13:53"