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In the context of SQL, data definition or data description language (DDL) is a syntax for creating and modifying database objects such as tables, indices, and users. DDL statements are similar to a computer programming language for defining data structures, especially database schemas. Common examples of DDL statements include CREATE, ALTER ...
The Data Definition Language (DDL) manages table and index structure. The most basic items of DDL are the CREATE , ALTER , RENAME , DROP and TRUNCATE statements: CREATE creates an object (a table, for example) in the database, e.g.:
The purpose of DQL commands is to get the schema relation based on the query passed to it. Although often considered part of DML, the SQL SELECT statement is strictly speaking an example of DQL. When adding FROM or WHERE data manipulators to the SELECT statement the statement is then considered part of the DML.
Data Definition Language (DDL) Data Control Language (DCL [2]) Transaction Control Language (TCL) DCL commands are used for access control and permission management for users in the database. With them we can easily allow or deny some actions for users on the tables or records (row level security). DCL commands are: GRANT
Application- or user-specific database objects in relational databases are usually created with data definition language (DDL) commands, which in SQL for example can be CREATE, ALTER and DROP. [4] [5] Rows or tuples from the database can represent objects in the sense of object-oriented programming, but are not considered database objects. [6]
In SQL, the data manipulation language comprises the SQL-data change statements, [3] which modify stored data but not the schema or database objects. Manipulation of persistent database objects, e.g., tables or stored procedures, via the SQL schema statements, [3] rather than the data stored within them, is considered to be part of a separate data definition language (DDL).
If the trigger is created on a schema or the database, then the triggering event is composed of either DDL or database operation statements, and the trigger is called a system trigger. An INSTEAD OF trigger is either: A DML trigger created on a view or a system trigger defined on a CREATE statement.
The terms data dictionary and data repository indicate a more general software utility than a catalogue. A catalogue is closely coupled with the DBMS software. It provides the information stored in it to the user and the DBA, but it is mainly accessed by the various software modules of the DBMS itself, such as DDL and DML compilers, the query optimiser, the transaction processor, report ...