数据库中的DDL/DML/DCL解释（转）

DDL is Data Definition Language statements. Some examples:数据定义语言，用于定义和管理 SQL 数据库中的所有对象的语言

1.CREATE - to create objects in the database 创建

2.ALTER - alters the structure of the database 修改

3.DROP - delete objects from the database 删除

4.TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed 清空

5.COMMENT - add comments to the data dictionary 注释

6.GRANT - gives user's access privileges to database 授权

7.REVOKE - withdraw access privileges given with the GRANT command 收回已经授予的权限

DML is Data Manipulation Language statements. Some examples:数据操作语言，SQL中处理数据等操作统称为数据操纵语言

1.SELECT - retrieve data from the a database 查询

2.INSERT - insert data into a table 添加

3.UPDATE - updates existing data within a table 更新

4.DELETE - deletes all records from a table, the space for the records remain 删除

5.CALL - call a PL/SQL or Java subprogram

6.EXPLAIN PLAN - explain access path to data

7.LOCK TABLE - control concurrency 锁，用于控制并发

DCL is Data Control Language statements. Some examples:数据控制语言，用来授予或回收访问数据库的某种特权，并控制数据库操纵事务发生的时间及效果，对数据库实行监视等

1.COMMIT - save work done 提交

2.SAVEPOINT - identify a point in a transaction to which you can later roll back 保存点

3.ROLLBACK - restore database to original since the last COMMIT 回滚

4.SET TRANSACTION - Change transaction options like what rollback segment to use 设置当前事务的特性，它对后面的事务没有影响．

以上解释如下图所示：

以上转自：http://blog.knowsky.com/221957.htm