The Components of SQL
IN THIS CHAPTER
SQL is a special-purpose language designed for the creation and maintenance of data in relational databases. Although the vendors of relational database management systems have their own SQL implementations, an ISO/IEC standard (revised in 2016) defines and controls what SQL is. All implementations differ from the standard to varying degrees. Close adherence to the standard is the key to running a database (and its associated applications) on more than one platform.
Although SQL isn’t a general-purpose programming language, it contains some impressive tools. Three languages within the language offer everything you need to create, modify, maintain, and provide security for a relational database:
- The Data Definition Language (DDL): The part of SQL that you use to create (completely define) a database, modify its structure, and destroy it when you no longer need it.
- The Data Manipulation Language (DML): The part of SQL that performs database maintenance. Using this powerful tool, you can specify what you want to do with the data in your database — enter it, change it, remove ...