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mysql 事务处理及表锁定深入简析

Jun 07, 2016 pm 05:55 PM
mysql transaction processing table lock

本文将详细介绍mysql 事务处理及表锁定,需要了解更多的朋友可以参考下

MYSQL的事务处理主要有两种方法。
1、用begin,rollback,commit来实现
begin 开始一个事务
rollback 事务回滚
commit 事务确认
2、直接用set来改变mysql的自动提交模式
MYSQL默认是自动提交的,也就是你提交一个QUERY,它就直接执行!我们可以通过
set autocommit=0 禁止自动提交
set autocommit=1 开启自动提交
来实现事务的处理。
当你用 set autocommit=0 的时候,你以后所有的SQL都将做为事务处理,直到你用commit确认或rollback结束。
注意当你结束这个事务的同时也开启了个新的事务!按第一种方法只将当前的作为一个事务!
个人推荐使用第一种方法!

MYSQL中只有INNODB和BDB类型的数据表才能支持事务处理!其他的类型是不支持的!
***:一般MYSQL数据库默认的引擎是MyISAM,这种引擎不支持事务!如果要让MYSQL支持事务,可以自己手动修改:
方法如下:
1.修改c:\appserv\mysql\my.ini文件,找到skip-InnoDB,在前面加上#,后保存文件。
2.在运行中输入:services.msc,重启mysql服务。
3.到phpmyadmin中,mysql->show engines;(或执行mysql->show variables like 'have_%'; ),查看InnoDB为YES,即表示数据库支持InnoDB了。
也就说明支持事务transaction了。
4.在创建表时,就可以为Storage Engine选择InnoDB引擎了。如果是以前创建的表,可以使用mysql->alter table table_name type=InnoDB;
或 mysql->alter table table_name engine=InnoDB;来改变数据表的引擎以支持事务。
以下是测试的实例代码
代码如下:
mysql_query("BEGIN"); //或者mysql_query("START TRANSACTION");
//若不使用事务,則$sql执行成功,$sql1执行失败
$sql = " insert into test values('11','88') ";
$sql1 = " insert into test values('11','88','444') ";
$res = mysql_query($sql);
$res1 = mysql_query($sql1);
//因为使用了事务,則兩個insert都执行失败
if($res && $res1){
mysql_query("COMMIT");
}
else{
mysql_query("ROLLBACK");
}
mysql_query("END");
mysql_query("SET AUTOCOMMIT=0"); //設置mysql不自動提交,需自行用commit語句提交
$sql = " insert into test values('11','88') ";
$sql1 = " insert into test values('11','88','444') ";
$res = mysql_query($sql);
$res1 = mysql_query($sql1);
//因为使用了事物,则两个insert都执行失败
if($res && $res1){
mysql_query("COMMIT");
}
else{
mysql_query("ROLLBACK");
}
mysql_query("END");

对于不支持事务的MyISAM引擎数据库可以使用表锁定的方法:
代码如下:
代码如下:
//MyISAM & InnoDB 都支持,
//Notes:query语句不能写在一起如:mysql_query("select * from a;select * from b;");
$sql_1=" LOCK TABLES test WRITE ";
mysql_query($sql_1);
$sql_2=" INSERT INTO test VALUES('".$a."','".$b."') ";
if(mysql_query($sql_2)){
echo 'successful!';
}else{
echo 'Unsuccessful!';
}
$sql_3=" UNLOCK TABLES ";
mysql_query($sql_3);
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