一 事务是什么？ 正常的sql语句是一条一条的执行，各个sql之间互不影响。 事务的机制类于一个黑盒，黑盒里的sql语句（多条）要么全部成功了，要么全部失败了。（土话就这么讲，术语我就不说了） 二 如何应用事务？ 一个事务有三个关键步骤：开始、提交、回滚
一 事务是什么？
正常的sql语句是一条一条的执行，各个sql之间互不影响。
事务的机制类似于一个黑盒，黑盒里的sql语句（多条）要么全部成功了，要么全部失败了。（土话就这么讲，术语我就不说了）
二 如何应用事务？
一个事务有三个关键步骤：开始、提交、回滚。
开始就是要告诉数据库我要开始事务了，那么数据库就会给你提供一个黑盒，接下来你就开始执行sql，如果sql都没问题，那么就执行提交，那么黑盒里操作的结果就会真正写入数据库，如果有失败的，那么执行以下回滚，数据库没有任何改变。
从这个角度看，黑盒更像是一个“沙盒”。
php想对应的是操作mysqli库的三个方法: mysqli::autocommit, mysqli::commit(), mysqli::rollback().
三 单元测试
1.创建mysql测试表（MyISAM引擎不支持事务，InnoDB引擎可以支持，所以将测试表建为InnoDB引擎）
表名：transaction_test，两个字段：id主键自增，content字符串类型。
<span>CREATE</span> <span>TABLE</span><span> `transaction_test`(
`id` </span><span>int</span>(<span><strong>11</strong></span>) <span>NOT</span> <span>NULL</span><span> AUTO_INCREMENT,
`content` </span><span>varchar</span>(<span><strong>256</strong></span>) <span>DEFAULT</span> <span>NULL</span><span>,
</span><span>PRIMARY</span> <span>KEY</span><span> (`id`)
) ENGINE</span><span>=</span>InnoDB <span>DEFAULT</span> CHARSET<span>=</span>utf8 COMMENT<span>=</span><span>'</span><span>php事务测试表</span><span>'</span>;
2.插入初始化数据
<span>insert</span> <span>into</span> transaction_test(content) <span>values</span>(<span>'</span><span>北京</span><span>'</span>),(<span>'</span><span>上海</span><span>'</span>),(<span>'</span><span>广州</span><span>'</span>);
如图：
3.php连接数据库并插入数据测试
创建transaction_test.php
<span>php
</span><span>$mysqli</span> = <span>new</span> mysqli("localhost", "root", "", "test"<span>);
</span><span>/*</span><span> check connection </span><span>*/</span>
<span>if</span> (<span>mysqli_connect_errno</span><span>()) {
</span><span>printf</span>("Connect failed: %s\n", <span>mysqli_connect_error</span><span>());
</span><span>exit</span><span>();
}
</span><span>/*</span><span> set charset </span><span>*/</span>
<span>$sql_set_charset</span> = "set names utf8"<span>;
</span><span>$query</span> = <span>$mysqli</span>->query(<span>$sql_set_charset</span><span>);
</span><span>if</span>(<span>$query</span>===<span>false</span><span>) {
</span><span>echo</span> 'set charset failed <br>'<span>;
</span><span>exit</span>(0<span>);
}
</span><span>/*</span><span> insert </span><span>*/</span>
<span>$sql_1</span> = "insert into transaction_test(`content`) values('天津')"<span>;
</span><span>$query1</span> = <span>$mysqli</span>->query(<span>$sql_1</span><span>);
</span><span>if</span>(<span>$query1</span>===<span>false</span><span>) {
</span><span>echo</span> 'query1 failed <br>'<span>;
} </span><span>else</span><span> {
</span><span>printf</span>("insert_id one: %d <br>", <span>$mysqli</span>-><span>insert_id);
}
</span><span>$mysqli</span>-><span>close();
</span>?>
运行效果及数据库结果：
插入OK。
4.测试mysqli::autocommit()。
autocommit()方法是设置数据库是否自动提交，参数为true和false，默认true。默认状态下每执行一次query()，数据库就会提交一次，那么如果设置为false,数据库就不会自动提交，那么就可以开始事务了，具体用法看下面的测试：
在上面代码的基础上，在插入数据的sql语句query之前，关闭自动提交。
<span>php
</span><span>$mysqli</span> = <span>new</span> mysqli("localhost", "root", "", "test"<span>);
</span><span>/*</span><span> check connection </span><span>*/</span>
<span>if</span> (<span>mysqli_connect_errno</span><span>()) {
</span><span>printf</span>("Connect failed: %s\n", <span>mysqli_connect_error</span><span>());
</span><span>exit</span><span>();
}
</span><span>/*</span><span> set charset </span><span>*/</span>
<span>$sql_set_charset</span> = "set names utf8"<span>;
</span><span>$query</span> = <span>$mysqli</span>->query(<span>$sql_set_charset</span><span>);
</span><span>if</span>(<span>$query</span>===<span>false</span><span>) {
</span><span>echo</span> 'set charset failed <br>'<span>;
</span><span>exit</span>(0<span>);
}
</span><span>/*</span><span> 关闭自动提交，开始事务 </span><span>*/</span>
<span>$mysqli</span>->autocommit(<span>false</span><span>);
</span><span>/*</span><span> insert </span><span>*/</span>
<span>$sql_1</span> = "insert into transaction_test(`content`) values('重庆')"<span>;
</span><span>$query1</span> = <span>$mysqli</span>->query(<span>$sql_1</span><span>);
</span><span>if</span>(<span>$query1</span>===<span>false</span><span>) {
</span><span>echo</span> 'query1 failed <br>'<span>;
} </span><span>else</span><span> {
</span><span>printf</span>("insert_id one: %d <br>", <span>$mysqli</span>-><span>insert_id);
}
</span><span>$mysqli</span>-><span>close();
</span>?>
运行效果及数据库结果：
分析：php返回id为5，但数据库却没有这条记录，说明开始事务之后所执行的query只是在一个“沙盒”里，并没有真正的写入到数据库。
5.测试mysqli::commit()
在上面代码中插入代码的后面加上commit()方法。
<span>php
</span><span>$mysqli</span> = <span>new</span> mysqli("localhost", "root", "", "test"<span>);
</span><span>/*</span><span> check connection </span><span>*/</span>
<span>if</span> (<span>mysqli_connect_errno</span><span>()) {
</span><span>printf</span>("Connect failed: %s\n", <span>mysqli_connect_error</span><span>());
</span><span>exit</span><span>();
}
</span><span>/*</span><span> set charset </span><span>*/</span>
<span>$sql_set_charset</span> = "set names utf8"<span>;
</span><span>$query</span> = <span>$mysqli</span>->query(<span>$sql_set_charset</span><span>);
</span><span>if</span>(<span>$query</span>===<span>false</span><span>) {
</span><span>echo</span> 'set charset failed <br>'<span>;
</span><span>exit</span>(0<span>);
}
</span><span>/*</span><span> 关闭自动提交，开始事务 </span><span>*/</span>
<span>$mysqli</span>->autocommit(<span>false</span><span>);
</span><span>/*</span><span> insert </span><span>*/</span>
<span>$sql_1</span> = "insert into transaction_test(`content`) values('哈尔滨')"<span>;
</span><span>$query1</span> = <span>$mysqli</span>->query(<span>$sql_1</span><span>);
</span><span>if</span>(<span>$query1</span>===<span>false</span><span>) {
</span><span>echo</span> 'query1 failed <br>'<span>;
} </span><span>else</span><span> {
</span><span>printf</span>("insert_id one: %d <br>", <span>$mysqli</span>-><span>insert_id);
}
</span><span>/*</span><span> 事务提交 </span><span>*/</span>
<span>$mysqli</span>-><span>commit();
</span><span>$mysqli</span>-><span>close();
</span>?>
运行效果及数据库结果：
分析：执行提交后数据就真正写入数据库了，另外通过id是6可以看出，刚才没有提交的事务虽然没有写入数据库，但是却消耗了一个自增的id。
6.测试mysqli::rollback()
将上面的commit()换成rollback()
<span>php
</span><span>$mysqli</span> = <span>new</span> mysqli("localhost", "root", "", "test"<span>);
</span><span>/*</span><span> check connection </span><span>*/</span>
<span>if</span> (<span>mysqli_connect_errno</span><span>()) {
</span><span>printf</span>("Connect failed: %s\n", <span>mysqli_connect_error</span><span>());
</span><span>exit</span><span>();
}
</span><span>/*</span><span> set charset </span><span>*/</span>
<span>$sql_set_charset</span> = "set names utf8"<span>;
</span><span>$query</span> = <span>$mysqli</span>->query(<span>$sql_set_charset</span><span>);
</span><span>if</span>(<span>$query</span>===<span>false</span><span>) {
</span><span>echo</span> 'set charset failed <br>'<span>;
</span><span>exit</span>(0<span>);
}
</span><span>/*</span><span> 关闭自动提交，开始事务 </span><span>*/</span>
<span>$mysqli</span>->autocommit(<span>false</span><span>);
</span><span>/*</span><span> insert </span><span>*/</span>
<span>$sql_1</span> = "insert into transaction_test(`content`) values('沈阳')"<span>;
</span><span>$query1</span> = <span>$mysqli</span>->query(<span>$sql_1</span><span>);
</span><span>if</span>(<span>$query1</span>===<span>false</span><span>) {
</span><span>echo</span> 'query1 failed <br>'<span>;
} </span><span>else</span><span> {
</span><span>printf</span>("insert_id one: %d <br>", <span>$mysqli</span>-><span>insert_id);
}
</span><span>/*</span><span> 事务回滚 </span><span>*/</span>
<span>$mysqli</span>-><span>rollback();
</span><span>$mysqli</span>-><span>close();
</span>?>
运行效果及数据库结果：
分析：同样是返回的id是7，但数据库没有插入这条记录。那这跟上面的不写rollback()的结果不是一样吗？肯定不一样，继续测试。
7.继续测试rollback()
把上面代码的rollback()去掉，在上面的insert语句的query之后，修改autocommit为true，因为一个事务完成之后还要执行其他的sql语句，要把自动提交恢复到默认状态，然后再执行一次insert语句。
<span>php
</span><span>$mysqli</span> = <span>new</span> mysqli("localhost", "root", "", "test"<span>);
</span><span>/*</span><span> check connection </span><span>*/</span>
<span>if</span> (<span>mysqli_connect_errno</span><span>()) {
</span><span>printf</span>("Connect failed: %s\n", <span>mysqli_connect_error</span><span>());
</span><span>exit</span><span>();
}
</span><span>/*</span><span> set charset </span><span>*/</span>
<span>$sql_set_charset</span> = "set names utf8"<span>;
</span><span>$query</span> = <span>$mysqli</span>->query(<span>$sql_set_charset</span><span>);
</span><span>if</span>(<span>$query</span>===<span>false</span><span>) {
</span><span>echo</span> 'set charset failed <br>'<span>;
</span><span>exit</span>(0<span>);
}
</span><span>/*</span><span> 关闭自动提交，开始事务 </span><span>*/</span>
<span>$mysqli</span>->autocommit(<span>false</span><span>);
</span><span>/*</span><span> insert </span><span>*/</span>
<span>$sql_1</span> = "insert into transaction_test(`content`) values('沈阳')"<span>;
</span><span>$query1</span> = <span>$mysqli</span>->query(<span>$sql_1</span><span>);
</span><span>if</span>(<span>$query1</span>===<span>false</span><span>) {
</span><span>echo</span> 'query1 failed <br>'<span>;
} </span><span>else</span><span> {
</span><span>printf</span>("insert_id one: %d <br>", <span>$mysqli</span>-><span>insert_id);
}
</span><span>/*</span><span> 事务回滚
$mysqli->rollback();
</span><span>*/</span>
<span>/*</span><span> 恢复自动提交 </span><span>*/</span>
<span>$mysqli</span>->autocommit(<span>true</span><span>);
</span><span>/*</span><span> insert </span><span>*/</span>
<span>$sql_2</span> = "insert into transaction_test(`content`) values('长春')"<span>;
</span><span>$query2</span> = <span>$mysqli</span>->query(<span>$sql_2</span><span>);
</span><span>if</span>(<span>$query2</span>===<span>false</span><span>) {
</span><span>echo</span> 'query2 failed <br>'<span>;
} </span><span>else</span><span> {
</span><span>printf</span>("insert_id two: %d <br>", <span>$mysqli</span>-><span>insert_id);
}
</span><span>$mysqli</span>-><span>close();
</span>?>
运行效果及数据库结果：
分析：虽然前面开启了事务，但是自动提交恢复默认之后，第一条insert语句同样写进了数据库，所以不写rollback()并没有回滚。
8 继续测试rollback()
将上面代码中的rollback()的注释去掉
<span>php
</span><span>$mysqli</span> = <span>new</span> mysqli("localhost", "root", "", "test"<span>);
</span><span>/*</span><span> check connection </span><span>*/</span>
<span>if</span> (<span>mysqli_connect_errno</span><span>()) {
</span><span>printf</span>("Connect failed: %s\n", <span>mysqli_connect_error</span><span>());
</span><span>exit</span><span>();
}
</span><span>/*</span><span> set charset </span><span>*/</span>
<span>$sql_set_charset</span> = "set names utf8"<span>;
</span><span>$query</span> = <span>$mysqli</span>->query(<span>$sql_set_charset</span><span>);
</span><span>if</span>(<span>$query</span>===<span>false</span><span>) {
</span><span>echo</span> 'set charset failed <br>'<span>;
</span><span>exit</span>(0<span>);
}
</span><span>/*</span><span> 关闭自动提交，开始事务 </span><span>*/</span>
<span>$mysqli</span>->autocommit(<span>false</span><span>);
</span><span>/*</span><span> insert </span><span>*/</span>
<span>$sql_1</span> = "insert into transaction_test(`content`) values('沈阳')"<span>;
</span><span>$query1</span> = <span>$mysqli</span>->query(<span>$sql_1</span><span>);
</span><span>if</span>(<span>$query1</span>===<span>false</span><span>) {
</span><span>echo</span> 'query1 failed <br>'<span>;
} </span><span>else</span><span> {
</span><span>printf</span>("insert_id one: %d <br>", <span>$mysqli</span>-><span>insert_id);
}
</span><span>/*</span><span> 事务回滚 </span><span>*/</span>
<span>$mysqli</span>-><span>rollback();
</span><span>/*</span><span> 恢复自动提交 </span><span>*/</span>
<span>$mysqli</span>->autocommit(<span>true</span><span>);
</span><span>/*</span><span> insert </span><span>*/</span>
<span>$sql_2</span> = "insert into transaction_test(`content`) values('长春')"<span>;
</span><span>$query2</span> = <span>$mysqli</span>->query(<span>$sql_2</span><span>);
</span><span>if</span>(<span>$query2</span>===<span>false</span><span>) {
</span><span>echo</span> 'query2 failed <br>'<span>;
} </span><span>else</span><span> {
</span><span>printf</span>("insert_id two: %d <br>", <span>$mysqli</span>-><span>insert_id);
}
</span><span>$mysqli</span>-><span>close();
</span>?>
运行效果及数据库结果：
分析：id为10的记录没有插入到数据库，这次执行回滚了。
--------------------------------------------------------------------------------------------------------------
9 基于以上的测试，应该对autocommit(),commit(),rollback()有一个比较深的认识了，最后贴一段代码模拟一下真实环境
<span> 1</span> <span>php
</span><span> 2</span> <span>$mysqli</span> = <span>new</span> mysqli("localhost", "root", "", "test"<span>);
</span><span> 3</span>
<span> 4</span> <span>/*</span><span> check connection </span><span>*/</span>
<span> 5</span> <span>if</span> (<span>mysqli_connect_errno</span><span>()) {
</span><span> 6</span> <span>printf</span>("Connect failed: %s\n", <span>mysqli_connect_error</span><span>());
</span><span> 7</span> <span>exit</span><span>();
</span><span> 8</span> <span>}
</span><span> 9</span>
<span>10</span> <span>/*</span><span> set charset </span><span>*/</span>
<span>11</span> <span>$sql_set_charset</span> = "set names utf8"<span>;
</span><span>12</span> <span>$query</span> = <span>$mysqli</span>->query(<span>$sql_set_charset</span><span>);
</span><span>13</span> <span>if</span>(<span>$query</span>===<span>false</span><span>) {
</span><span>14</span> <span>echo</span> 'set charset failed <br>'<span>;
</span><span>15</span> <span>exit</span>(0<span>);
</span><span>16</span> <span>}
</span><span>17</span>
<span>18</span> <span>/*</span><span> 关闭自动提交，开始事务 </span><span>*/</span>
<span>19</span> <span>$mysqli</span>->autocommit(<span>false</span><span>);
</span><span>20</span>
<span>21</span> <span>/*</span><span> insert </span><span>*/</span>
<span>22</span> <span>$commit</span> = <span>true</span><span>;
</span><span>23</span> <span>$sql_array</span> = <span>array</span>("insert into transaction_test(`content`) values('石家庄')","insert into transaction_test(`content2`) values('郑州')"<span>);
</span><span>24</span> <span>foreach</span>(<span>$sql_array</span> <span>as</span> <span>$key</span>=><span>$item</span><span>) {
</span><span>25</span> <span>$query</span> = <span>$mysqli</span>->query(<span>$item</span><span>);
</span><span>26</span> <span>if</span>(<span>$query</span>===<span>false</span><span>) {
</span><span>27</span> <span>/*</span><span> 事务回滚 </span><span>*/</span>
<span>28</span> <span>printf</span>("query failed : %d <br>", <span>$key</span><span>);
</span><span>29</span> <span>$mysqli</span>-><span>rollback();
</span><span>30</span> <span>$commit</span> = <span>false</span><span>;
</span><span>31</span> <span>break</span><span>;
</span><span>32</span> } <span>else</span><span> {
</span><span>33</span> <span>printf</span>("insert_id <span>$key</span>: %d <br>", <span>$mysqli</span>-><span>insert_id);
</span><span>34</span> <span> }
</span><span>35</span> <span>}
</span><span>36</span>
<span>37</span> <span>/*</span><span> 提交事务 </span><span>*/</span>
<span>38</span> <span>if</span>(<span>$commit</span><span>) {
</span><span>39</span> <span>$mysqli</span>-><span>commit();
</span><span>40</span> <span>}
</span><span>41</span>
<span>42</span> <span>/*</span><span> 恢复自动提交 </span><span>*/</span>
<span>43</span> <span>$mysqli</span>->autocommit(<span>true</span><span>);
</span><span>44</span>
<span>45</span> <span>/*</span><span> insert </span><span>*/</span>
<span>46</span> <span>$sql_2</span> = "insert into transaction_test(`content`) values('最后插入')"<span>;
</span><span>47</span> <span>$query2</span> = <span>$mysqli</span>->query(<span>$sql_2</span><span>);
</span><span>48</span> <span>if</span>(<span>$query2</span>===<span>false</span><span>) {
</span><span>49</span> <span>echo</span> 'query2 failed <br>'<span>;
</span><span>50</span> } <span>else</span><span> {
</span><span>51</span> <span>printf</span>("insert_id two: %d <br>", <span>$mysqli</span>-><span>insert_id);
</span><span>52</span> <span>}
</span><span>53</span>
<span>54</span> <span>$mysqli</span>-><span>close();
</span><span>55</span> ?>
分析：上面的代码中23行的两条sql语句都是正确的，测试的时候可以这样测：两条都正确，1正确2不正确，1不正确2正确，1和2都不正确。
结果：（只有两条都正确的时候才会真正写入数据库，其他3种情况都回滚了）
更广阔的的天地就靠大家发挥了。
貌似这里php的人少，.net人要多一点，希望写的有用。
作者：老默http://www.cnblogs.com/laomo/
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