Wikibooks: MySQL/Language/Definitions: what are DDL, DML and DQL?

• Format: Book
• Language: English
• Subjects: DML
• Online Access: https://en.wikibooks.org/wiki/MySQL/Language/Definitions:_what_are_DDL,_DML_and_DQL%3F

Data Definition Language (DDL) refers to the CREATE ALTER and DROP statements. DDL or Data Definition Language actually consists of the SQL commands that can be used to define the database schema. DDL allows to add / modify / delete the logical structures which contain the data or which allow users to access / maintain the data (databases tables keys views.). DDL is about metadata . Data Manipulation Language (DML) refers to the INSERT UPDATE and DELETE statements DML allows to add / modify / delete data itself. Data Query Language (DQL) refers to the SELECT SHOW and HELP statements (queries) SELECT is the main DQL instruction. It retrieves data you need. SHOW retrieves infos about the metadata. HELP. is for people who need help. Data Control Language (DCL) refers to the GRANT and REVOKE statements DCL is used to grant / revoke permissions on databases and their contents. DCL is simple but MySQL s permissions are rather complex. DCL is about security. Data Transaction Language (DTL) refers to the START TRANSACTION SAVEPOINT COMMIT and ROLLBACK [TO SAVEPOINT] statements DTL is used to manage transactions (operations which include more instructions none of which can be executed if one of them fails). BookCat