1. Multiple Table Queries
A Guide to SQL – Chapter 5

2. Instructional Objectives
Use joins to retrieve data from one than one table
Use IN and EXISTS operators to query multiple tables
Use a subquery within a subquery
ALL
ANY

3. Joining tables
Used when dealing with multiple tables (rather than writing lengthy subqueries)
Finds rows in two tables that have identical values in matching columns
Example:
List the number and name of each customer along with the number, last name, and first name of the sales rep who represents the customer. Sort the records by customer number.

4. Solution
SELECT CustomerNum, CustomerName, Rep.RepNum, LastName, FirstName
FROM Customer, Rep
WHERE Customer.RepNum = Rep.RepNum
ORDER BY CustomerNum;

5. Another example
Lists the number and name of each customer whose credit limit is $7,500 together with the number, last name, and first name of the sales rep who represents the customer

6. Solution
SELECT Customer_Num, Customer_Name, Rep.Rep_Num, Last_Name, First_Name
FROM Customer, Rep
WHERE Customer.Rep_Num = Rep.Rep_Num
AND Credit_Limit = 7500;

7. Example
For every part on order, list the order number, part number, part description, number of units ordered, quoted price, and unit price
Solution:
SELECT Order_Num, Order_Line.Part_Num, Description, Num_Ordered, Quoted_Price, Price
FROM Order_Line, Part
WHERE Order_Line.Part_Num = Part.Part_Num;

8. Example
Find the description of each part included in order number 21610
Solution:
SELECT Description
FROM Order_Line, Part
WHERE Order_Line.Part_Num = Part.Part_Num
AND Order_Num = ‘21610’;

9. Another way… IN Operator
SELECT Description
FROM Part
WHERE Part_Num IN
(SELECT Part_Num
FROM Order_Line
WHERE Order_Num = ‘21610’);

10. Your Turn
List all the number and dates of those orders that include a part located in warehouse 3

11. Solution

12. Alternate solution… subquery within a subquery
Find the order number and order date for each order that includes a part located in warehouse 3
Solution:
SELECT Order_Num, Order_Date
FROM Orders
WHERE Order_Num IN
(SELECTOrder_Num
FROM Order_Line
WHERE Part_Num IN
(SELECT Part_Num
FROM Part
WHERE Warehouse = ‘3’));

13. Exists Can also be used to get data from multiple tables
Checks for existence of rows that satisfy some criterion
Example:
Find the order number and order date for each order that contains part number DR93

14. Solution:

15. Your turn
For every order, list the order number, order date, customer number, and customer name. In addition, for each order line within the order, list the part number, description, number ordered, and quoted price. Sort the records by order number.

16. Solution

17. Comprehensive Example… Your Turn
List the customer number, order number, and order total for each order with a total that exceeds $1,000. Rename the order total as ORDER_TOTAL

18. Solution…
SELECT Customer_Num, Orders.Order_Num, SUM(Num_Ordered * Quoted_Price) AS ORDER_TOTAL
FROM Orders, Order_Line
WHERE Orders.Order_Num = Order_Line.Order_Num
GROUP BY Orders.Order_Num, Customer_Num
HAVING Sum (Num_Ordered * Quoted_Price) > 1000
Order By Orders.Order_Num;

19. Joining a table to itself (self-join)
Have to use an alias (in FROM clause) to treat a table as two tables.
Example:
For each pair of customers located in the same city, display the customer number, customer name, and city

20. Solution
(See figures 5.12 & 5.13 on p )

21. Set Operations Union Intersect (intersection) Minus (difference)
Of two tables is a temp table containing every row that is in either the first table, the second table or both
Intersect (intersection)
Of two tables is a temp table containing all rows that are in both tables
Tables must be union compatible – same number of columns with identical data types and lengths
Minus (difference)
Of two tables is (a temp table) the set of all rows that are in the first table but not in the second table
Access does not support Intersect or Minus

22. Union example
List the number and name of each customer that either is represented by sales rep 65 or that currently has orders on file, or both
Solution:

23. Intersect example
List the number and name of each customer that is represented by sales rep 65 and that currently has orders on file
Solution:
Since Access does not support Intersect, use subquery

24. Minus Example
List the number and name of each customer that is represented by sales rep 65 and that does not currently have orders on file
Solution:
Since Access does not support Intersect, use subquery

25. ALL
Find the customer number, name, current balance, and rep number of each customer whose balance is greater than the individual balances of each customer of sales rep 65.
Solution:

26. ANY
Find the customer number, name, current balance, and rep number of each customer whose balance is greater than the balance of at least one customer of sales rep 65.
Solution:

27. Special Operations Inner join Outer join
Join that compares the tables in the FROM clause and lists only those rows that satisfy the condition
All the examples we have looked at so far have used inner joins
Outer join
Used to list all rows from one of the tables in a join, regardless of whether they match any rows in the other table
Types of outer join
Left outer join
Right outer join
Full outer join

28. Outer joins Left outer join Right outer join Full outer join
All rows from the table on the left will be included regardless of whether they match rows from the table on the right
Right outer join
All rows from the table on the right will be included regardless of whether they match rows from the table on the left
Full outer join
All rows from both tables will be included regardless of whether they match rows from the other table

29. Outer join example
Display the customer number, customer name, order number, and order date for all orders. Include all customers in the results. For customer that do not have orders, omit the order number and order date.

30. Outer join example solution

31. Product
Combination of all rows in the first table and all rows in the second table
Example:
Form the product of the Customer and Orders table. Display the customer number, name, order number and order date
Solution: