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：
