sql - 什么是 DDL 和 DML？

Question

我听说过有关数据库的术语 DDL 和 DML，但我不明白它们是什么。

它们是什么以及它们与 SQL 有何关系？

Answer 1

以下内容改编自这里MySQL What is DDL, DML and DCL? :

DDL

DDL is short name of Data Definition Language, which deals withdatabase schemas and descriptions, of how the data should reside inthe database.

• CREATE – to create database and its objects like (table, index, views, store procedure, function and triggers).
• ALTER – alters the structure of the existing database.
• DROP – delete objects from the database.
• TRUNCATE – remove all records from a table; also, all spaces allocated for the records are removed.
• COMMENT – add comments to the data dictionary.
• RENAME – rename an object.

DML

DML is short name of Data Manipulation Language which deals with datamanipulation, and includes most common SQL statements such SELECT,INSERT, UPDATE, DELETE etc, and it is used to store, modify, retrieve,delete and update data in database.

• SELECT – retrieve data from one or more tables.
• INSERT – insert data into a table.
• UPDATE – updates existing data within a table.
• DELETE – delete all records from a table.
• MERGE – UPSERT operation (insert or update)
• CALL – call a PL/SQL or Java subprogram.
• EXPLAIN PLAN – interpretation of the data access path.
• LOCK TABLE – concurrency control.

DCL

DCL is short name of Data Control Language which includes commandssuch as GRANT, and mostly concerned with rights, permissions and othercontrols of the database system.

• GRANT – allow users access privileges to database.
• REVOKE – withdraw users access privileges given by using the GRANT command.

TCL

TCL is short name of Transaction Control Language which deals withtransaction within a database.

• COMMIT – commits a transaction.
• ROLLBACK – rollback a transaction in case of any error occurs.
• SAVEPOINT – a point inside a transaction that allows rollback state to what it was at the time of the savepoint.
• SET TRANSACTION – specify characteristics for the transaction.