php - 事务内的Mysql事务

Question

在一个使用 mysql 数据库的 PHP 脚本中，我最近需要在恰好位于另一个事务中的某个点使用一个事务。我所有的测试似乎都表明这很好，但我找不到任何关于这种用法的文档。

我想确定——事务中的事务在 mysql 中是否有效？如果是这样，有没有办法找出嵌套事务的深度有多少？ (即恢复正常需要多少回滚)

提前致谢，布赖恩

Answer 1

与其他人的答案相反，您可以在交易中有效地创建交易，这真的很容易。您只需创建 SAVEPOINT 位置并使用 ROLLBACK TO savepoint 来回滚部分事务，其中 savepoint 是您为保存点指定的任何名称。MySQL 文档链接:http://dev.mysql.com/doc/refman/5.0/en/savepoint.html当然，事务中任何地方的查询都不应该是隐式提交的类型，否则将提交整个事务。

例子:

START TRANSACTION;

# queries that don't implicitly commit

SAVEPOINT savepoint1;

# queries that don't implicitly commit

# now you can either ROLLBACK TO savepoint1, or just ROLLBACK to reverse the entire transaction.

SAVEPOINT savepoint2;

# queries that don't implicitly commit

# now you can ROLLBACK TO savepoint1 OR savepoint2, or ROLLBACK all the way.
# e.g.

ROLLBACK TO savepoint1;
COMMIT; # results in committing only the part of the transaction up to savepoint1

我在 PHP 中写过这样的代码，而且效果很好:

foreach($some_data as $key => $sub_array) {
  $result = mysql_query('START TRANSACTION'); // note mysql_query is deprecated in favor of PDO
  $rollback_all = false; // set to true to undo whole transaction
  for($i=0;$i<sizeof($sub_array);$i++) {
    if($sub_array['set_save'] === true) {
      $savepoint = 'savepoint' . $i;
      $result = mysql_query("SAVEPOINT $savepoint");
    }
    $sql = 'UPDATE `my_table` SET `x` = `y` WHERE `z` < `n`'; // some query/queries
    $result = mysql_query($sql); // run the update query/queries

    $more_sql = 'SELECT `x` FROM `my_table`'; // get data for checking
    $result = mysql_query($more_sql);
    
    $rollback_to_save = false; // set to true to undo to last savepoint
    while($row = mysql_fetch_array($result)) {
      // run some checks on the data
      if( /*some check says to go back to savepoint */) {
        $rollback_to_save = true; // or just do the rollback here.
      }
      if( /* some check says to rollback entire transaction */ ) {
        $rollback_all = true;
      }
    }
    if($rollback_all === true) {
      mysql_query('ROLLBACK'); // rollback entire transaction
      break; // break out of for loop, into next foreach
    }
    if($rollback_to_save = true) {
      mysql_query("ROLLBACK TO $savepoint"); // undo just this part of for loop
    }
  } // end of for loop
  mysql_query('COMMIT'); // if you don't do this, the whole transaction will rollback
}