错误：SELECT email FROM users WHERE email = 'dhruv@gmail.com' 在进行查询时收到此错误 [重复]

Question

嘿，我正在填写注册表，这是我的代码

if (isset($_POST['submit'])) {
    $GST = $_POST['GST'];
    $email = $_POST['email'];
     $contact = $_POST['contact'];
  $whatsapp = $_POST['whatsapp'];
     $adhaar = $_POST['adhaar'];
     $username = $_POST['username'];
     $password = $_POST['password'];
     $pan = $_POST['pan'];
     $district = $_POST['district'];
// Define variables and initialize with empty values



$sql = "SELECT email FROM users WHERE email = '$email'";
$result = mysqli_query($con, $sql);

if (mysqli_num_rows($result) == 1) {
    echo "string";
}else{
    $sql2 = "INSERT INTO users (username, password,email,district,gst,watsapp,adhaar,contact,pan) VALUES ($username, $password,$email,$district,$GST,$whatsapp,$adhaar,$contact,$pan)";

    if (mysqli_query($con, $sql2)) {
   $customername = $_POST['product_name'];
   foreach ($customername as $key => $value) {//start ho rah hai
       $sql = "INSERT INTO center (id) VAlues ('$value')";
       if (mysqli_query($con, $sql)) {
    echo "string";
}
   }// khatam ho rha hai ye 
}else{
 echo "Error: " . $sql . "<br>" . mysqli_error($con);
}

}



}

   ?>

我收到此错误错误：SELECT email FROM users WHERE email = 'dhruv@gmail.com'

如果我不使用此代码

$customername = $_POST['product_name'];
   foreach ($customername as $key => $value) {//start ho rah hai
       $sql = "INSERT INTO center (id) VAlues ('$value')";
       if (mysqli_query($con, $sql)) {
    echo "string";
}

然后它显示没有错误我无法理解发生了什么。

Answer 1

使用 MySQL，字符串比较不像其他代码那样工作。基本上，您不能使用= 来做您认为的事情。当这种情况发生时，MySQL 会用它做其他事情。

阅读this MySQL 中的字符串操作手册以获得更多帮助，但您想使用关键字LIKE 并与电子邮件地址完全匹配，例如：

WHERE email LIKE '$email'"

您可能需要使用 PHP MySQL 转义字符串函数过滤 @ here

注意*

您的代码目前容易受到 MySQL 注入的攻击。接受用户输入并直接输入数据库查询是非常危险的，也是一种不好的做法。

阅读更多here 以了解如何预防。