php - 准备好的语句错误

Question

在调试过程中，我注意到脚本死于 $stmt->fetch() 或 die($stmt->error); 行。 PHP 日志中没有错误。它也不会回显任何错误。您是否看到代码中有任何错误的部分？

$stmt = $db->prepare("SELECT e.msg_subject AS subject, e.msg_text AS text, u.fname AS firstname, u.lname AS lastname FROM emails AS e, users AS u WHERE e.msg_status=? AND e.msg_type=? AND u.id=?") or die($db->error);
    $stmt->bind_param("isi", $status, $type, $userid) or die($stmt->error);
    $stmt->execute() or die($stmt->error);
    $stmt->bind_result($subject, $text, $firstname, $lastname) or die($stmt->error);
    $stmt->fetch() or die($stmt->error);
    $stmt->close();

Answer 1

问题在于，如果 SQL 语句未检索到任何行，$stmt->fetch() 将返回 bool 值 FALSE。因此，您必须检查行数:

if ($stmt->num_rows > 0) {
    $stmt->fetch() or die($stmt->error);
}