SQL Pocket GuideOld Books SQL is the language of databases. It's used to create and maintain database objects, place data into those objects, query the data, modify the data, and, finally, delete data that is no longer needed. Databases lie at the heart of many, if not most business applications. Chances are very good that if you're involved with software development, you're using SQL to some degree. And if you're using SQL, you should own a good reference or two.