It is not possible, in a book on EJB technology, to provide a detailed description of relational databases and SQL. If you are unfamiliar with database technology, the brief overview that follows may be enough to get you started, but at some point you will almost certainly need to spend some time reading about SQL, particularly if you intend to use entity EJBs with bean-managed persistence (see Chapter 12).
The documentation that comes with the Cloudscape database— supplied with the J2EE Reference Implementation—is a good place to start reading about SQL in more detail, and it’s free. Nice one, Informix.
SQL (Structured Query Language) is a language for querying and updating the data on relational database servers. ...