Chapter 3

The Components of SQL


Bullet Creating databases

Bullet Manipulating data

Bullet Protecting databases

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 ...

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