SQL Clearly Explained, 2nd Edition

11. Keeping the Design Up to Date

One of the benefits that relational DBMSs have over DBMSs based on older data models is that the schema is easy to change. As long as a table isnapos;t being used at the time you want to modify it, its design can be changed without affecting other tables in the database. (This is said with the caveat that the presence of foreign key constraints may prevent some deletions and modifications or cause other modifications to occur.) The SQL statements that modify database structures are therefore an important part of a database administrator's arsenal. In this chapter, weapos;ll look at the types of changes that can be made and how to make them.

Modifying Tables

With the exception of tables, structural database elements ...