Introduction






Introduction

The UPDATE, INSERT, and DELETE statements update the contents of a table. With SQL, we can also change the structure of a table, even when that table contains millions of rows. We can add columns, change the data type of an existing column, add integrity constraints, and can even delete entire tables. This chapter describes all the features to drop tables (with the DROP TABLE statement), to rename them (the RENAME statement), and to change them (the ALTER TABLE statement).

Note

In most examples in this book, we assume that each table contains its original contents. If you execute the statements in this chapter with SQL, you change the structure and the contents, of course. Because of this, the results of your statements in the following examples could differ from those in the book. On the Web site of the book, www.r20.nl, you can find information on how the tables can be restored to their original state.




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