Designing tables that many applications will use is a critical task. Table design can be difficult because you can represent the same information in many different ways. “Chapter 4. Designing objects and relationships” covers some of the issues that you need to consider when you make decisions about table design.
You create tables by using the SQL CREATE TABLE statement. At some point after you create and start using your tables, you might need to make changes to them. The ALTER TABLE statement lets you add and change columns, add or drop a primary key or foreign key, add or drop table check constraints, or add and change partitions. Carefully consider design changes to avoid or reduce the disruption to your applications.