如何将mysql_num_rows等功能更改为mysqli？

Question

我将PHP文件启动到免费的虚拟主机站点时遇到错误。显示的错误如下：

下面是我的项目的代码。

    $sql= "SELECT * FROM user WHERE staff_id='$staff_id' AND password='$password'";
    $query = mysql_query($sql) or die("Error: " . mysql_error());  //this is error on line 42
    $row = mysql_num_rows($query);

我不确定错误是什么，因为我是在PHP上自学的。希望你们能指出我应该做出的改变。预先感谢！

Answer 1

    $sql= "SELECT * FROM user WHERE staff_id='$staff_id' AND password='$password'";
$query = mysql_query($sql) or die("Error: " . mysql_error());  //this is error on line 42
$row = mysql_num_rows($query);

尝试这个

$sql= "SELECT * FROM user WHERE staff_id='$staff_id' AND password='$password'";
$query = mysqli_query($con, $sql) or die("Error: " . mysqli_error($con)); // $con is the connection to database like  // $con = mysqli_connect("localhost","my_user","my_password","my_db");
$row = mysqli_num_rows($query);

Answer 2

首先，正如您在标题中所建议的那样，出于安全原因，甚至更好地使用PDO，请使用mysqli。

使用mysqli：（已更新）

$stmt = $conn->prepare("SELECT COUNT(*) FROM user WHERE staff_id = :staff_id AND password = :password");
$res = $stmt->execute(["staff_id" => $staff_id, "password" => $password);
$row = mysqli_num_rows($res);

使用PDO：

$stmt = $conn->prepare("SELECT COUNT(*) FROM user WHERE staff_id = :staff_id AND password = :password");
$res = $stmt->execute(["staff_id" => $staff_id, "password" => $password);
$row = $res->fetchColumn();

$conn是您的数据库链接。 PDO版本假定您不需要行，而只需要计数。如果有人告诉您，请勿在{{1​​}}查询中使用rowCount，这是不可靠的。