Top-Down SQL Tuning

Answer 1

Note that Order_Types is never referenced!

There is no join to T!!

SELECT DISTINCT O.Order_ID, O.Order_Date, C.Name, L.Line_ID, L.Quantity, I.Name

FROM Orders O, Order_Types T, Order_Lines L, Items I, Customers C

WHERE O.Customer_ID = :B1

AND L.Order_ID = O.Order_ID

AND I.Item_ID = L.Item_ID

AND C.Customer_ID = O.Customer_ID;