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SQL – Part II

SQL – Part II. Yong Choi School of Business CSU, Bakersfield. 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(*). Example 18 SQL Query to Count Records.

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SQL – Part II

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  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(*)

  3. Example 18 SQL Query to Count Records

  4. Example 18 SELECTcount(*) FROM Part WHERE Class="HW";

  5. SQL Examples – Aggregate Functions • Example 19: Save as example 19 • Find the number of customers and the total of their balances. • Calculate total: sum(field name)

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

  7. Example 19 SELECT count(*), Sum(Balance) 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 BalancesTotal. • Change column name using “AS” command

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

  10. Example 20 SELECT count(*) AS CustomerCount, Sum(Balance) AS BalanceTotal 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. • Think about connection between tables (OrderLine and Part).

  12. Example 21 SQL Query with Subquery

  13. Example 21 SELECT OrderNum FROM OrderLine WHERE PartNum IN (SELECT PartNum FROM Part WHERE Warehouse='3');

  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

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

  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.

  18. Example 23 SQL Query to Restrict Groups

  19. Example 23 SELECTRepNum, count(*) AS NumCustomer, Avg(Balance) AS AverageBalance FROM Customer GROUP BYRepNum HAVINGCount(*)<4;

  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 SELECTRepNum, count(*) AS NumCustomer, Avg(Balance) AS AverageBalance FROM Customer WHERECreditLimit<10000 GROUP BYRepNum HAVINGCount(*)<3;

  23. SQL Examples – Joining Tables • Use of multiple 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. • CustomerNum, CustomerName, RepNum, LastName, FirstName

  24. Example 24 SQL Query to Join Tables

  25. Example 24 SELECT CustomerNum, CustomerName, Rep.RepNum, LastName, FirstName FROM Customer, Rep WHERERep.RepNum=Customer.RepNum;

  26. 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.

  27. Example 25 Query to Restrict Records in Join

  28. Example 25 SELECT CustomerNum, CustomerName, Rep.RepNum, LastName, FirstName FROM Customer, Rep WHERE Rep.RepNum=Customer.RepNum ANDCreditLimit=10000;

  29. 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. • How many tables? • How many conditions?

  30. Example 26 Query to Join Multiple Tables

  31. Example 26 SELECTOrders.OrderNum, Orderdate, Customer.CustomerNum, CustomerName, Part.PartNum, Description, NumOrdered, QuotedPrice FROM Orders, Customer, OrderLine, Part WHERECustomer.CustomerNum=Order.CustomerNumANDOrder.OrderNum=OrderLine.OrderNum AND OrderLine.PartNum=Part.PartNum;

  32. 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 or that currently have orders on file, or both.

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

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

  35. 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.

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

  37. 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';

  38. 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';

  39. 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

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

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

  42. 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).

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

  44. 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)

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

  46. SQL Examples – Creating a New Table Using a Existing Table • Example 31: save as example 31 • Create a new table named SmallCust, consisting of all fields from the Customer table and those rows in which the credit limit is less than or equal to $7,500. SELECT INTO Name of table to create FROM WHERE

  47. Example 31 SQL Query to Create New Table

  48. Example 31 SELECT * INTO SmallCust FROM Customer WHERE CreditLimit<=7500;

  49. SQL - Data Definition I • Create a database structure to hold all the database tables; MS Access ONLY can create tables • Usually, only a DBA can create a new database structure • SQL syntax for creating a database structure: • CREATE SCHEMA AUTHORIZATION <creator>; • Example:CREATE SCHEMA AUTHORIZATION JONES;

  50. SQL - Data Definition II • Specify a new relation by giving it a name and specifying each of its attributes. • Each attribute is given a name, a data type to specify its values, and some constraints on the attribute. • Syntax: CREATE TABLE <table name>;

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