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SQL Sublanguages

DDL (Data Definition Language)​

DDL commands define and manage the structure of a database, i.e. its tables, columns, constraints, and indexes.

Common commands:

  • CREATE — creates a new table, view, index, or database
  • ALTER — modifies an existing structure (e.g. adding or removing a column)
  • DROP — permanently deletes a table or database
  • TRUNCATE — removes all rows from a table without deleting the table itself

DML (Data Manipulation Language)​

DML commands are used to modify the actual stored data.

Common commands:

  • INSERT — adds new rows to a table
  • UPDATE — modifies existing rows
  • DELETE — removes rows from a table

DQL (Data Query Language)​

DQL is used to query and retrieve data from the database without modifying it.

Common commands:

  • SELECT — retrieves rows from one or more tables, optionally filtered, grouped, or sorted

DCL (Data Control Language)​

DCL manages access rights and permissions for database users.

Common commands:

  • GRANT — gives a user permission to perform specific actions
  • REVOKE — removes previously granted permissions