错误提示如下：SQLSTATE[HY000]: 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.这是什么原因？谢谢
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http://www.flashj.cn/wp/pdo-transaction-err-in-php.html
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If you do not fetch all of the data in a result set before issuing your next call to PDO::query(), your call may fail. Call PDOStatement::closeCursor() to release the database resources associated with the PDOStatement object before issuing your next call to PDO::query().
再次查询，要释放掉之前的查询。正如错误提示所说的：Consider using PDOStatement::fetchAll()