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
    • Overview of Data Manipulation
    • Populating Tables with New Data
    • Updating Existing Data
    • Deleting Data from Tables
    • Summary
    • Q&A
    • Workshop
  • 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
  • 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

Deleting Data from Tables

The DELETE command is used to remove entire rows of data from a table. The DELETE command is not used to remove values from specific columns; a full record, including all columns, is removed. The DELETE statement must be used with caution—as it works all too well. The next section discusses methods for deleting data from tables.

To delete a single record or selected records from a table, the DELETE statement must be used with the following syntax:

   
delete from table_name
[where condition];

   DELETE FROM ORDERS_TBL

   WHERE ORD_NUM = '23A16';
   
1 row deleted.

Notice the use of the WHERE clause. The WHERE clause is an essential part of the DELETE statement if you are attempting to remove selected rows of data from a table. You rarely issue a DELETE statement without the use of the WHERE clause. If you do, your results will be similar to the following example:

DELETE FROM ORDERS_TBL; 

11 rows deleted.

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