PDO 查询一半时间返回 False答案

【问题标题】：PDO query returning False half the timePDO 查询一半时间返回 False
【发布时间】：2011-07-06 13:07:38
【问题描述】：

我对 PDO mysql 查询有疑问

这是我的简单代码（不是真实情况，只是为了向您展示问题）

$connexion = new PDO(SQL_DSN, SQL_USERNAME, SQL_PASSWORD);
$stmt = $connexion->prepare('SELECT * from missions,platforms WHERE missions_platforms_id = exl_platforms_id AND missions_id = :mission');
$stmt->execute(array(":mission" => '1'));
$ligne = $stmt->fetch(PDO::FETCH_ASSOC);
var_dump($stmt);

$stmt = $connexion->prepare('SELECT * from missions,platforms WHERE missions_platforms_id = exl_platforms_id AND missions_id = :mission');
var_dump($stmt);
$stmt = $connexion->prepare('SELECT * from missions,platforms WHERE missions_platforms_id = exl_platforms_id AND missions_id = :mission');
var_dump($stmt);

和输出：

object(PDOStatement)[2]
 public 'queryString' => string 'SELECT * from missions,platforms WHERE missions_platforms_id = platforms_id AND missions_id = :mission' (length=122)

boolean false

object(PDOStatement)[2]
 public 'queryString' => string 'SELECT * from missions,platforms WHERE missions_platforms_id = platforms_id AND missions_id = :mission' (length=122)

为什么第二个 var_dump 返回 false ？

如果我多次执行相同的架构，则一半时间返回 false...

谢谢你

【问题讨论】：

是否打印了任何 PHP 错误？尝试在该代码之前添加error_reporting(E_ALL | E_STRICT); ini_set('display_errors', true);。
还可以尝试添加 PDO::errorInfo 调用 - 请参阅此处的示例：php.net/manual/en/pdo.errorinfo.php
在其他无缓冲查询处于活动状态时无法执行查询。考虑使用 PDOStatement::fetchAll()。或者，如果您的代码只针对 mysql 运行，您可以通过设置 PDO::MYSQL_ATTR_USE_BUFFERED_QUERY 属性来启用查询缓冲。谢谢迈克！

标签： php mysql pdo prepare

【解决方案1】：

在使用PDOStatement::fetch() 读取结果集后尝试关闭结果集游标PDOStatement::closeCursor() 例如：

$connexion = new PDO(SQL_DSN, SQL_USERNAME, SQL_PASSWORD);
$stmt = $connexion->prepare('SELECT * from missions,platforms WHERE missions_platforms_id = exl_platforms_id AND missions_id = :mission');
$stmt->execute(array(":mission" => '1'));
$ligne = $stmt->fetch(PDO::FETCH_ASSOC);
var_dump($stmt);
$stmt->closeCursor();

$stmt = $connexion->prepare('SELECT * from missions,platforms WHERE missions_platforms_id = exl_platforms_id AND missions_id = :mission');
var_dump($stmt);
$stmt = $connexion->prepare('SELECT * from missions,platforms WHERE missions_platforms_id = exl_platforms_id AND missions_id = :mission');
var_dump($stmt);

第一个语句是您实际从中获取结果的唯一语句。

【讨论】：