douhuan2101
2017-02-06 22:48 阅读 77
已采纳

Mysqli_num_rows问题

First the code

mysqli_free_result($wynik);

$query = mysqli_query($dbcon, "SELECT * FROM user WHERE login = '$login' AND password ='$pass'");

$sql = mysqli_num_rows($query) 
        or die(drop dead);

echo $sql;

if ($sql > 0) {

                $_SESSION['user'] = $login;
                $_SESSION['auth'] = TRUE;
                echo $login;

I have a small issue with this code. When $query finds a result everything works fine, but when it returns no results $sql part dies. I can't understand why. When i run the query in database it works fine and returns 0 results.

  • 点赞
  • 写回答
  • 关注问题
  • 收藏
  • 复制链接分享

2条回答 默认 最新

  • 已采纳
    doubo1711 doubo1711 2017-02-06 22:53

    Because when you get no rows, you basically get 0 or die(). 0 is "falsy", so your die is executed. You don't want a die() there, basically just remove it.

    $sql = mysqli_num_rows($query); // Don't use die() for this
    

    See this live demo.


    It's more common to use or die() after the query, although it's not the best handling of errors, this is probably where you've seen it before

    $query = mysqli_query($dbcon, "SELECT * FROM user WHERE login = '$login' AND password ='$pass'") or die ("Query failed ".mysqli_error($dbcon));
    

    Also you should look into prepared statements to protect your database against SQL injection. See the links given below.

    点赞 评论 复制链接分享
  • dragon8837 dragon8837 2017-02-06 22:59

    or die() isn't some special error-handing feature of PHP. It actually performs a logical OR on the left and right values. It's commonly used to handle errors with functions that return a 0 on error because it's a short circuit operator. That means that it only evaluates the second operand if the first one is not a "True" value ( see How does true/false work in PHP? for info on how true/false is handled in PHP).

    What's happening here is $sql = sqli_num_rows($query) or die() is the same as $sql = 0 or die(). Since 0 is a false value, it tries to evaluate the die() and dies.

    点赞 评论 复制链接分享

相关推荐