Commands included in DDL DML DQL DCL in SQL
The definitions and scope of application of DDL, DML, DQL, and DCL are as follows:
-
Data Definition Language (DDL) :
DDL is used to create, modify, and delete objects such as tables, views, and indexes in the database. Its main commands include CREATE, ALTER and DROP, etc. DDL statements are used to define the structure of the database, such as creating tables, defining columns and constraints, etc. Note: DDL is implicitly committed and does not support transactions.
-
Data Manipulation Language (DML) :
DML is used to insert, update and delete data in the database. The main commands include INSERT, UPDATE and DELETE. DML allows users to insert new records into a table, update existing records, or delete specific records.
-
Data Query Language (DQL) :
DQL is used to get the required data from the database. Its main command is SELECT, which is used to select all data in a specific column or table. DQL allows users to filter data based on specific conditions, such as using a WHERE clause to define filter conditions.
-
Data Control Language (DCL) :
DCL is used to grant or revoke user access to database objects and manage database security. The main commands include GRANT and REVOKE, which are used to grant and revoke access permissions. DCL can also be used to manage user accounts, roles and permissions.
These classifications are intended to clearly distinguish the different functions and purposes of the SQL language. DQL is mainly used to query and retrieve data, DDL is used to define the database structure, DML is used to manipulate data, and DCL is used to manage database access rights and security. Through this classification, the SQL language provides a concise and unified method to operate and manage relational database systems.