PostgreSQL, Second Edition

Sequences

One problem that you will most likely encounter in your database life is the need to generate unique identifiers. We've already seen one example of this in the customers table—the customer_id column is nothing more than a unique identifier. Sometimes, an entity that you want to store in your database will have a naturally unique identifier. For example, if you are designing a database to track employee information (in the United States), a Social Security number might make a good identifier. Of course, if you employ people who are not U.S. citizens, the Social Security number scheme will fail. If you are tracking information about automobiles, you might be tempted to use the license plate number as a unique identifier. That would work ...