Sample Data Description Language › About This Appendix

About This Appendix

Up to now, you have been using SQL DML statements to retrieve or update data. You haven't been concerned with table design or layout, and you have had full access to all tables. This appendix shows how a system administrator might use DDL to define a database and users' access to it. If you use SQL against a multi-user database, your use can be affected by decisions made by the system administrator who:

• Creates databases and tables using SQL DDL
• Specifies which database the tables are associated with and identifies the physical files in which to store data
• Defines constraints on the data so that only valid data is stored in the database
• Restricts access to tables and creates views of them

Each of these functions can have an impact on the way you access data from tables.

No Online Exercises

There are no online exercises in this chapter. Please do not enter any of the statements online.