SQL语言分类

SQL语言主要有以下几类：

1. 数据查询语言: Data Query Language。select语句，用于检索数据库数据。
2. 数据操纵语言: Data Manipulation Language,DML。 用于改变数据库数据，包括insert(插入）、update（更新）、delete（删除）三条语句。
3. 数据定义语言：Data Definition Language,DDL。用于建立、修改、和删除数据库对象。包括create(创建）、alter(修改）、drop(删除）。DDL语句会自动提交事务。
4. 事务控制语言：Transactional Control Language,TCL。用于维护数据的一致性，包括commit(提交）、rollback（回滚）、savepoint(保存点）
5. 数据控制语言：Data Control Language，DCL。用于执行权限授予和权限回收操作，包括grant(授予）、revoke（撤销）。DCL语句也是自动对事务进行提交。

DML : insert、update、delete  (select) 实践中常把查询语言和数据操纵语言作为同义词使用，技术上来说是不正确的。

DDL：create、alter、drop

DCL：grant、revoke

TCL：commit、rollback、savepoint

附加DDL,DML,DCL区别： 
DDL is Data Definition Language statements. Some examples: 

* CREATE - to create objects in the database 
* ALTER - alters the structure of the database 
* DROP - delete objects from the database 
* TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed 
* COMMENT - add comments to the data dictionary 
* GRANT - gives user's access privileges to database 
* REVOKE - withdraw access privileges given with the GRANT command 

DML is Data Manipulation Language statements. Some examples: 

* SELECT - retrieve data from the a database 
* INSERT - insert data into a table 
* UPDATE - updates existing data within a table 
* DELETE - deletes all records from a table, the space for the records remain 
* CALL - call a PL/SQL or Java subprogram 
* EXPLAIN PLAN - explain access path to data 
* LOCK TABLE - control concurrency 

DCL is Data Control Language statements. Some examples: 

* COMMIT - save work done 
* SAVEPOINT - identify a point in a transaction to which you can later roll back 
* ROLLBACK - restore database to original since the last COMMIT 
* SET TRANSACTION - Change transaction options like what rollback segment to use