SQL – Part II

1. SQL – Part II Yong Choi School of Business CSU, Bakersfield

2. SQL Examples – Aggregate Functions • Example 18: Save as example 18 • How many parts (count number of records) are in item class HW? • Use of “count” command • Count all records: count(*) • No idea? Try to figure out manually!

3. Example 18 SQL Query to Count Records

4. Example 18 SELECT count(*) FROM Part WHERE Class=_____________;

5. SQL Examples – Aggregate Functions • Example 19: Save as example 19 • Find the number of customers and the total of their balances.

6. Example 19 SQL Query to Count Records and Calculate a Total

7. Example 19 SELECT count(*), Sum(____________) FROM Customer;

8. SQL Examples – Aggregate Functions • Example 20: Save as example 20 • Find the total number of customers and the total of their balances. Change the column names for the number of customers and the total of their balances to CustomerCount and BalanceTotal. • Assign column name using “AS” command

9. Example 20 SQL Query to Perform Calculations and Rename Fields

10. Example 20 SELECT count(*) AS ___________, Sum(Balance) AS _____________ FROM Customer;

11. SQL Examples – Nested Query • A query inside another query • A inside query (sub-query) is evaluated first. It is common to enclose sub-query in parentheses for readability!! • Example 21: Save as example 21 • List the order number for each order from the order line table for a part located in warehouse 3. That is, we are looking for list of OrderNum that is associated with warehouse 3. • No idea? Try to figure out manually!

12. Example 21 SQL Query with Subquery

13. Example 21 SELECT OrderNum FROM OrderLine WHERE PartNum IN (SELECT ___________ FROM ___________ WHERE ___________);

14. SQL Examples - Grouping • Use GROUP BY clause • ONLY grouping, NOT sorting (usually associated with ORDER BY clause) • Example 22: Save as example 22 • For each sales rep, list the rep number, the number of customers assigned to each rep, and the average balance of the rep’s customers. • Rename the count of the number of customers and the average of the balances to NumOfCustomers and AverageBalance

15. Example 22 SQL Query to Group Records # of customers are grouped by each sales rep #

16. Example 22 SELECT RepNum, Count(_____) AS NumOfCustomer, Avg(Balance) AS AvgBalance FROM Customer GROUP BY ____________;

17. SQL Examples – Grouping (con’t) • Example 23: Save as example 23 • For each sales rep with fewer than four customers, list the rep number, the number of customers assigned to the rep, and the average balance of the rep’s customers. Rename the count of the number of customers and the average of the balances to NumOfCustomers and AverageBalance. • Use of “Having” command. • Count, Rep. with < 4 customers (group)

18. Example 23 SQL Query to Restrict Groups • # of customers are grouped by each sales rep # • Apply the condition to the group

19. Example 23 • where to put “Having” command? SELECTRepNum, count(*) AS NumCustomer, Avg(Balance) AS AverageBalance FROM Customer GROUP BYRepNum;

20. SQL Examples – Grouping (con’t) • Use of Where and Having clauses together • “Where” command must be stated first • Example 23-1: Save as example 23-1 • Exactly same as example 23. Except, only groups with fewer than three records and customers with credit limit of less than $10,000 must be included.

21. Example 23-1 SQL Query with ‘WHERE’ and ‘HAVING’ Clauses

22. Example 23-1 • Where to put “Where” command? SELECT RepNum, count(*) AS NumCustomer, Avg(Balance) AS AverageBalance FROM Customer GROUP BY RepNum HAVINGCount(*)<3;

23. Exercise Question 8 from chapter 6 • How many students are enrolled on Database and Networking? (Hint: use SectionNo for each class so you can determine the answer from the semester of 2008)? • Which courses were taught in the first semester of 2008 (I-2008) but not in the second semester of 2008 (II-2008)? (Note: There is no indication of the second semester of 2008 (II-2008))?

24. Matching Field • Try below SQLs using Matching_DB on the class website • To identify missing “RepNum,” make sure to review each table first! SQL 1 SELECT Customer.RepNum, CustomerName, Rep.RepNum, LastName, FirstName FROM Customer, Rep; SQL 2 SELECT Customer.RepNum, CustomerName, Rep.RepNum, LastName, FirstName FROM Customer, Rep Where Customer.RepNum=Rep.RepNum;

25. Inner Join Example • For each customer who placed an order, what is the customer’s name and order number? The best way to find out match customers with their orders is Including CustumerID from both tables

27. Different Type of SQL Joins • (INNER) JOIN: Returns records that have matching values in both tables • LEFT (OUTER) JOIN: Return all records from the left table, and the matched records from the right table • RIGHT (OUTER) JOIN: Return all records from the right table, and the matched records from the left table • FULL (OUTER) JOIN: Return all records when there is a match in either left or right table • Also, review SQL Joins in the textbook chapter 7

28. SQL Examples – Joining Tables • Example 24: Save as example 24 • List the number and name of each customer together with the number, last name, and first name of the sales rep who represents the customer. If a customer does not have a Rep., then he/she must not be included. • That is, look for matching RepNum from both tables

29. Example 24 SQL Query to Join Tables

30. Example 24 SELECT CustomerNum, CustomerName, Rep.RepNum, LastName, FirstName FROM Customer, Rep Where _______.RepNum =_________.RepNum; SELECT CustomerNum, CustomerName, Rep.RepNum, LastName, FirstName FROM Customer INNER JOIN [Rep] ON ________.RepNum=________.RepNum;

31. SQL Examples – Joining Tables (con’t) • Use of multiple tables with a compound condition • Example 25: Save as example 25 • List the number and name of each customer whose credit limit is $10,000 together with number, last name, and first name of the sales rep who represents the customer.

32. Example 25 Query to Restrict Records in Join

33. Example 25 SELECT CustomerNum, CustomerName, Rep.RepNum, LastName, FirstName FROM Customer, Rep WHERE Rep.RepNum=Customer.RepNum AND _______________________;

34. SQL Examples – Joining Tables (con’t) • Example 26: Save as example • 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. Make sure that everything is matched. In other words, any “unmatched” records must not be included.

35. Example 26 Query to Join Multiple Tables

36. Example 26 SELECT Orders.OrderNum, Orderdate, Customer.CustomerNum, CustomerName, Part.PartNum, Description, NumOrdered, QuotedPrice FROM Orders, Customer, OrderLine, Part WHERE Customer.CustomerNum=Orders.CustomerNum AND Orders.OrderNum=OrderLine.OrderNum AND OrderLine.PartNum=Part.PartNum;

37. SQL Examples – Union • The union of two tables is a table containing all rows that are in either the first table, the second table, or both tables. • Two tables involved in union must have same structure. • Example 27: Save as example 27 • List the number and name of all customers that are either represented by sales rep 35 ORthat currently have orders on file, ORboth. • Any “unmatched” records must not be included.

38. Example 27 SQL Query to Perform Union Red:Currently have orders on file Blue:Represented by sales rep 35 Green:Both

39. Example 27 SELECT CustomerNum, CustomerName FROM Customer WHERE RepNum='35' UNION SELECT Customer.CustomerNum, CustomerName FROM Customer, Orders WHERE Customer.CustomerNum=Orders.CustomerNum;

40. Three Basic Functions by SQLAnd Their Basic SQL Commands • Data definition (last topic) through the use of CREATE • Data manipulation(next topic) through INSERT, UPDATE, and DELETE • Data querying(we are done with this) through the use of SELECT AND MANY OTHERS, which is the basis for all SQL queries.

41. SQL - Data Manipulation • Possible with Access • UPDATE • INSERT • DELETE • Only possible with enterprise level DBMS • COMMIT • ROLLBACK

42. SQL - Data Manipulation (con’t) • UPDATE command makes data entry corrections UPDATE Project SET PrjtLocat = 'Bellaire', DeptNum = 5 WHERE PrjtNum = 10; UPDATE Employee SET Salary = Salary * 1.1 WHERE Branch = 'Lincoln';

43. SQL - Data Manipulation (con’t) • INSERT command add new data to a table INSERT INTO Employee (SSN, LastName, FirstName) VALUES ('Richard', 'Marini', '43433'); • DELETE command removes table row • DELETE FROM Employee • WHERE LastName = 'Brown';

44. SQL - Data Manipulation (con’t) • COMMIT command store data on the secondary memory permanently • ROLLBACK command restores database back to previous condition if COMMIT hasn’t been used

45. SQL Examples - Data Manipulation • Example 28:Save as example 28 • Update the street address of customer 524 to 1445 Rivard • First, review the current street address of customer 524 (838 Ridgeland)

46. Example 28 UPDATE Customer SET Street = '1445 Rivard' WHERE CustomerNum='524';

47. SQL Examples - Data Manipulation • Example 29: Save as example 29 • Add a new sales rep to the Rep table. Her number is 16, her name is Sharon Rands, and her address is 826 Raymond, Altonville, FL 32543. She has not yet earned any commission, but her commission rate is 5%(0.05). • First, review the “Rep” table

48. Example 29 INSERT INTO Rep VALUES ('16', 'Rands', 'Shron', '826 Raymond', 'Altonville', 'FL', '32543', 0, 0.05);

49. SQL Examples - Data Manipulation • Example 30: Save as example 30 • Delete any row in the Orderline table in which the part number is BV06 • First, review the part number BV06 (OrderNum21617)

50. Example 30 DELETE * FROM OrderLine WHERE PartNum='BV06';