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truncate table(截断表) 是清空一个表，是一个DDL语言，效率高，它与delete有如下区别：
* delete是DML语言;
* delete时会触发与表相关的触发器，而truncate不会;
* delete可以有删除条件，truncate没有。
在Oracle中如果删除了表中的某一条数据，还可以通过回滚操作(rollback)进行回滚，假如想清空一张表的数据，但是又不想使其能进行回滚操作，就可以立刻释放资源，这时就需要使用截断表了。它的主要功能就是彻底删除数据，使其不能进行回滚。这里我打个比方大家就立刻能明了它的作用。大家众所周知，当我们在自己的
PC（person computer
）上删除某一个文件，它并没有彻底删除而是进入了回收站，你要在回收站中再将其删除才算彻底清除。截断表就相当于直接将数据从pc上删除，而不会放入回收站。
截断表格式：
truncate table 表名
假如我们创建了一个tb_AW表
create tabletb_AW( name varchar(10), sex varchar(2) default '女' );
插入数据
insert into tb_AW(name,sex) values('Joe','男'); insert into tb_AW(name,sex)
values('周欣红','女');
查看表:
select *from tb_AW
现在进行截断
truncate table tb_AW
为了确定表格是否已释放，我们回滚查看下
rollback
输出结果：
注意这里回滚后，无法查到tb_AW表中的信息了，说明它已经彻底删除了，这就是截断表的功能。
虽然我们在操作中不会经常使用，但作为一个小知识点，可以去了解下。
