MySql的事务操作与示例_MySQL
事务就是一个逻辑工作单元的一系列步骤。事务是用来保证数据操作的安全性
事务的特征:
Atomicity(原子性)
Consistency(稳定性,一致性)
Isolation(隔离性)
Durability(可靠性)
【事务只针对对数据数据产生影响的语句有效】
show engines //查看mysql锁支持的数据引擎
MyISAM不支持事物,InnoDB支持事物
默认情况下,MySQL将以自动提交模式运行,这意味着没一条小命令都将当做一个只有一条命令的事物来执行。
如果要让mysql支持支持事务,只需要修改数据引擎(alter table person type=INNODB)
使用start transaction或者begin命令来开启一个事物,使用commit,或者rollback来结束事物。
事物的结束:事物除了commit,rollback会结束外,使用DDL或者DCL语句也会结束。
保存点:通过保存点机制:用户可以在事物里用savepoint name命令设置一些保存点,以后用户在使用rollback to savepoint name结束事物时,name之前的数据保存,之后的数据不保存。
mysql使用事务的关键字
1.begin //打开一个事务
2.commit //提交到数据库
3.rollback //取消操作
4.savepoint //保存,部分取消,部分提交
alter table person type=INNODB //修改数据引擎
示例:
begin
update person set name='efgh' where id =10
select * from person
rollback
select * from person
示例:
alter table person type=INNODB
begin
update person set name='efgh' where id =10
select * from person
commit
select * from person
begin
delete from person where id=21
update person set name='efgh' where id =10
commit/rollback
针对上面部分提交,必须用到保存点
保存点注意:
1.只能取消到某个保存点 rollback to savepoint p1
2.不能提交某个保存 commit to savepoint p2//错误写法
3.最后commit 把未取消的保存点去不提交到数据
事务保存点使用例子
1. begin;
2. update score set score=40 where scoreid=1;
3. savepoint s1;
4. update score set score=50 where scoreid=2;
5. select * from score;
6. rollback to savepoint s1;
7. select * from score;
8. commit;

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