PDO :: Query()返回false

Question

我正在尝试在PHP中学习和使用PDO.我在query()方法中遇到了一个问题.

我试图用来$sth = $db->query("SELECT * FROM titles ORDER BY RAND() LIMIT 1");随机选择一个网站的标题,但由于某种原因,$sth总是假的.它的工作原理,当我用prepare()和execute(),但我试图找到什么是错的query().

这是我正在调用的整个函数:

function getTitle($db)
    {
    if($db)
        {
            $db->exec("USE " . $dbsite); 
            $sth = $db->query("SELECT * FROM titles ORDER BY RAND() LIMIT 1");
            $title = $sth->fetch(PDO::FETCH_ASSOC);

            $db->exec("UPDATE titles SET count = count + 1 WHERE id = " . $title['id']);

            return $title['title'];
        }
    else
            return 'Home - Database Offline';

}

Answer 1

使用PDO的errorinfo()功能找出原因.

if( ! $sth = $db->query("SELECT * FROM titles ORDER BY RAND() LIMIT 1") ) {
  die(var_export($db->errorinfo(), TRUE));
}

晚更新

为了使我的旧答案更好,设置PDO以在错误上抛出异常比检查每个函数返回更容易管理.

$dbh = new PDO($connstr, $user, $pwd);
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

或者,更简洁:

$dbh = new PDO($connstr, $user, $pwd, [PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION]);