yii General error: 2014 Cannot execute queries while other unbuffered queries are active

yii 在使用事务时请注意。

$command  = Yii::app()->db->createCommand($sql);

$command ->execute();
$command->getPdoStatement()->closeCursor();  

$transaction->commit();

$command->getPdoStatement()->closeCursor();  这句很关键，如果没有这句，事务提交就会报错

General error: 2014 Cannot execute queries while other unbuffered queries are active.  Consider using PDOStatement::fetchAll().  Alternatively, if your code is only ever going to run against mysql, you may enable query buffering by setting the PDO::MYSQL_ATTR_USE_BUFFERED_QUERY attribute