Sams Teach Yourself SQL in 24 Hours

By Ron Plew and Ryan Stephens

• Table of Contents
  • Copyright
  • About the Authors
  • Acknowledgments
  • Tell Us What You Think!
  • Introduction
  • Part I: A SQL Concepts Overview
  • Hour 1. Welcome to the World of SQL
  • Part II: Building Your Database
  • Hour 2. Defining Data Structures
  • Hour 3. Managing Database Objects
  • Hour 4. The Normalization Process
  • Hour 5. Manipulating Data
  • Hour 6. Managing Database Transactions
  • Part III: Getting Effective Results from Queries
  • Hour 7. Introduction to the Database Query
  • Hour 8. Using Operators to Categorize Data
  • Hour 9. Summarizing Data Results from a Query
  • Hour 10. Sorting and Grouping Data
    • Why Group Data?
    • The GROUP BY Clause
    • GROUP BY Versus ORDER BY
    • The HAVING Clause
    • Summary
    • Q&A
    • Workshop
  • Hour 11. Restructuring the Appearance of Data
  • Hour 12. Understanding Dates and Times
  • Part IV: Building Sophisticated Database Queries
  • Hour 13. Joining Tables in Queries
  • Hour 14. Using Subqueries to Define Unknown Data
  • Hour 15. Combining Multiple Queries into One
  • Part V: SQL Performance Tuning
  • Hour 16. Using Indexes to Improve Performance
  • Hour 17. Improving Database Performance
  • Part VI: Using SQL to Manage Users and Security
  • Hour 18. Managing Database Users
  • Hour 19. Managing Database Security
  • Part VII: Summarized Data Structures
  • Hour 20. Creating and Using Views and Synonyms
  • Hour 21. Working with the System Catalog
  • Part VIII: Applying SQL Fundamentals in Today's World
  • Hour 22. Advanced SQL Topics
  • Hour 23. Extending SQL to the Enterprise, the Internet, and the Intranet
  • Hour 24. Extensions to Standard SQL
  • Part IX: Appendixes
  • Appendix A. Common SQL Commands
  • Appendix B. Using MySQL for Exercises
  • Appendix C. Answers to Quizzes and Exercises
  • Appendix D. CREATE TABLE Statements for Book Examples
  • Appendix E. INSERT Statements for Data in Book Examples
  • Appendix F. Glossary
  • Appendix G. Bonus Exercises

Workshop

The following workshop is composed of a series of quiz questions and practical exercises. The quiz questions are designed to test your overall understanding of the current material. The practical exercises are intended to afford you the opportunity to apply the concepts discussed during the current hour, as well as build upon the knowledge acquired in previous hours of study. Please take time to complete the quiz questions and exercises before continuing. Refer to Appendix C,"Answers to Quizzes and Exercises," for answers.

Quiz

1. Will the following SQL statements work?

   1. SELECT SUM(SALARY), EMP_ID 
      FROM EMPLOYEE_PAY_TBL
      GROUP BY 1 and 2;
      

   2. SELECT EMP_ID, MAX(SALARY) 
      FROM EMPLOYEE_PAY_TBL
      GROUP BY SALARY, EMP_ID;
      

   3. SELECT EMP_ID, COUNT(SALARY) 
      FROM EMPLOYEE_PAY_TBL
      ORDER BY EMP_ID
      GROUP BY SALARY;
      

2. True or false: You must also use the GROUP BY clause when using the HAVING clause.

3. True or false: The following SQL statement returns a total of the salaries by groups:

   SELECT SUM(SALARY) 
   FROM EMPLOYEE_PAY_TBL;
   

4. True or false: The columns selected must appear in the GROUP BY clause in the same order.

5. True or false: The HAVING clause tells the GROUP BY which groups to include.

Exercises

1. Invoke mysql.exe on your computer, and then type use learnsql; at the mysql> prompt.

2. Enter the following query at the mysql> prompt to show all cities in EMPLOYEE_TBL:

   
                  SELECT CITY
   
                  FROM EMPLOYEE_TBL;
   
               

3. Now, enter the following query and compare the results to the query in exercise 2:

   
                  SELECT CITY, COUNT(*)
   
                  FROM EMPLOYEE_TBL
   
                  GROUP BY CITY;
   
               

4. The HAVING clause works like the WHERE clause in that is allows the user to specify conditions on data returned. The WHERE clause is the main filter on the query and the HAVING clause is the filter used after groups of data have been established using the GROUP BY clause. Enter the following query to see how the HAVING clause works:

   SELECT CITY, COUNT(*) 
   FROM EMPLOYEE_TBL
   GROUP BY CITY
   HAVING COUNT(*) > 1;
   

5. Modify the query in exercise 3 to order the results in descending order, from highest count to lowest.

6. Write a query to list the average pay rate by position from the EMPLOYEE_PAY_TBL table.

7. Write a query to list the average salary by position from the EMPLOYEE_PAY_TBL table.

Share This