如何在PHP中与多个用户进行身份验证？

Question

I am creating a login page with help of php and mysql . I am having problem on authenticating when multiple user data stored in database . Suppose i have table with two user data

s.no  username  password
1      user1      1234
2      user2      234

when I am giving username and password of first serial no then there is no problem but when i am giving username user1 and password 234 . then user2 is getting authenticated... how to match username and password row wise?? I am providing my backend code.

I tried to print the query result ,it seems its changing username according to password entered.

enter code here
$result = mysqli_query($con,"select * from users where 
username='$username' and password ='$password'")
or die("Failed to connect to database".mysql_error());

$row = mysqli_fetch_array($result);


if ($row['username'] == $username && $row['password'] == $password)  
{   
    if($username=='user1')
    {
        header('Location:htm1/forms.php');
        echo "Login successful!!! Welcome ".$row['username'];
    }
    elseif($username=='user2')
    {
        header('Location:../php/index.php');
    }
else{'
   echo"failed";
}

i expect when i enter user1 and password doesn't mach with password of user1 then it should say login failed