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8 2: Define a Database Using SQL Data Definition Language Engineering LibreTexts

It simply deals with descriptions of the database schema and is used to create and modify the structure of database objects in the database. DDL is a set of SQL commands used to create, modify, and delete database structures but not data. These commands are normally not used by a general user, who should be accessing the database via an application. It is mainly used to modify and establish the structure of the objects present in a database by dealing with the database schema descriptions.

  • It does this through the use of commands such as COMMIT, ROLLBACK, SAVEPOINT, and SET TRANSACTION.
  • Structured Query Language, or SQL, is a comprehensive language for manipulating databases.
  • The Alter command can add up an additional column, drop the existing columns and even change the data types of various columns involved in a DB table.
  • Thus, once a certain object is destroyed, there would be no way at all to recover it.
  • Transaction Control Language commands are used to manage transactions in the database.

Thus, the database system implements integrity constraints that can be tested with minimal overhead. Many data description languages use a declarative syntax to define columns and data types. These statements can be freely mixed with other SQL statements, making the DDL not a separate language. (DDL) is used to create and modify the structure of objects in a database using predefined commands and a specific syntax.

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The action you just performed triggered the security solution. There are several actions that could trigger this block including submitting a certain word or basis sql phrase, a SQL command or malformed data. These commands have far more features than listed above and their specific syntax tends to vary among SQL dialects.

In some database environments, we can run more than one command at a time. The commands would be located in a file and would be submitted as a batch to be executed. DML (Data Manipulation Language) commands need to be commited/rolled back. DDL is short name of Data Definition Language, which deals with
database schemas and descriptions, of how the data should reside in
the database.

SQL Functions

Data Query Language (DQL) is used to get data within the schema objects of a database and also to query it and impose order upon it. It lets users get data from a database table and perform some operation on it. When the statement is executed, the result is compiled into a temporary table and displayed by the front-end program or application. Since DDL includes SQL statements to define changes in the database schema, it is considered a subset of SQL. SQL uses normal English verbs to modify database objects, and DDL does not appear as a different language in a SQL database.

Data Definition Language

The database system checks these constraints every time the database is updated. In general, a constraint can be an arbitrary predicate pertaining to the database. However, arbitrary predicates may be costly to the test.