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
  • 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
    • Advanced Topics
    • Cursors
    • Stored Procedures and Functions
    • Triggers
    • Dynamic SQL
    • Call-Level Interface
    • Using SQL to Generate SQL
    • Direct Versus Embedded SQL
    • Summary
    • Q&A
    • Workshop
  • 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

Using SQL to Generate SQL

Using SQL to generate SQL is a very valuable time-budgeting method of writing SQL statements. Assume you have 100 users in the database already. A new role, ENABLE (a user-defined object that is granted privileges), has been created and must be granted to those 100 users. Instead of manually creating 100 GRANT statements, the following SQL statement generates each of those statements for you:

   
SELECT 'GRANT ENABLE TO '|| USERNAME||';'
FROM SYS.DBA_USERS;

This example uses Oracle's system catalog view (which contains information for users).

Notice the use of single quotation marks around GRANT ENABLE TO. The use of single quotation marks allows whatever is between the marks (including spaces) to be literal. Remember that literal values can be selected from tables, the same as columns from a table. USERNAME is the column in the system catalog table SYS.DBA_USERS. The double pipe signs (||) are used to concatenate the columns. The use of double pipes followed by ';' concatenates the semicolon to the end of the username, thus completing the statement.

The results of the SQL statement look like the following:

GRANT ENABLE TO RRPLEW; 
GRANT ENABLE TO RKSTEP;

These results should be spooled to a file, which can be sent to the database. The database, in turn, executes each SQL statement in the file, saving you many keystrokes and much time. The GRANT ENABLE TO USERNAME; statement is repeated once for every user in the database.

Next time you are writing SQL statements and have repeated the same statement several times, allow your imagination to take hold and let SQL do the work for you.

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