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
    • What Is a Transaction?
    • What Is Transactional Control?
    • Transactional Control and Database Performance
    • Summary
    • Q&A
    • Workshop
  • 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
  • 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

Q&A

1. Is it necessary to issue a commit after every INSERT statement?

   No, absolutely not. If you were inserting a few hundred thousand rows into a table, a COMMIT would be recommended every 5,000–10,000 rows, depending on the size of the temporary rollback area (seek the advice of your database administrator). Remember that the database may freeze up or not function properly when the rollback area fills up.

2. How does the ROLLBACK command undo a transaction?

   The ROLLBACK command clears all changes from the rollback area.

3. If I issue a transaction and 99 percent of the transaction completes but the other 1 percent errs, will I be able to redo only the error part?

   No, the entire transaction must succeed; otherwise, data integrity is compromised.

4. A transaction is permanent after I issue a COMMIT, but can't I change data with an update?

   Permanent used in this matter means that it is now a part of the database. The UPDATE statement can always be used to make modifications or corrections to the data.

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