未知列'；电子邮件'；在where子句中

我对这段代码有问题。它在where子句中给了我"未知列"电子邮件"。我几乎什么都试过了，但我不知道问题出在哪里。我是初学者，所以请温柔：）

有什么解决办法吗？

非常感谢

    session_start();
    include('connect.php');
    if(isset($_POST['submit']))
    //when isn't username in form
    if($_POST['firstname'] == '')
    {
        $_SESSION['error']['firstname'] = 'First name is required';
    }
    if($_POST['surname'] == '')
    {
        $_SESSION['error']['surname'] = 'Surname is required';
    }
    //when email isn't in form
    if($_POST['email'] == '')
    {
        $_SESSION['error']['email'] = 'Email is required';
    }
    //check if is email in correct format
    if(preg_match("/^([a-zA-Z0-9])+([a-zA-Z0-9._-])*@([a-zA-Z0-9_-])+([a-zA-Z0-9._-]+)+$/", $_POST['email']))
    {
        //email is in correct format and exist?
        $email = $_POST['email'];
        $sql1 = "SELECT * FROM users WHERE email = '$email'";
        $result1 = mysqli_query($connect, $sql1) or  die(mysqli_error($connect));
        if(mysqli_num_rows($result1) > 0)
        {
            $_SESSION['error']['email'] = 'Email is already used';
        }
    }
    else
    //error for wrong format of email
    {
        $_SESSION['error']['email'] = 'Your email is in wrong format';
    }
    //when isn't password in form
if($_POST['password'] == '')
{
    $_SESSION['error']['password'] = 'Password is required';
}
//when is error -> registration form
/*if(isset($_SESSION['error']))
{
    header("Location: index.php");
    exit();
}
else
*/
{
    $firstname = mysqli_real_escape_string($connect,$_POST['firstname']);
    $surname = mysqli_real_escape_string($connect,$_POST['surname']);
    $email = $_POST['email'];
    $password =  mysqli_real_escape_string($connect,$_POST['password']);
    $phone_number = mysqli_real_escape_string($connect,$_POST['phone_number']);
    $note = mysqli_real_escape_string($connect,$_POST['note']);
    $sql2 = "INSERT INTO users (firstname, surname, email, phone_number, note, password) VALUES ('$firstname', '$surname',
    '$email', '$phone_number', '$note','$password')";
    $result2 = mysqli_query($connect, $sql2) or die('Error: ' .mysqli_error($connect));