PHP内部连接超过2个表

Question

I have 2 tables one for the login id, username, password and rank and the other one is for account status. I need to join the tables to execute only all the active accounts. Everytime I try my code in phpmyadmin it works fine but in my system it won't work. Is there anything problem with my code? Btw. rank is for account verfication if you are an administartor or student.

$sql = "SELECT a.login_id,username,password,rank,b.status FROM login2 as a    INNER JOIN login_stat2 as b ON a.login_id = b.login_id WHERE username     ='".$username."' AND password='".$pass."' AND b.status='ACTIVE'";

$result = mysqli_query($con,$sql)or die(mysqli_error($con));
while($row = mysqli_num_rows($result));
session_regenerate_id();
        $member = mysqli_fetch_assoc($result);
        $_SESSION['SESS_MEMBER_ID'] = $member['login_id'];
        $_SESSION['SESS_NAME']      = $member['username'];
        $_SESSION['SESS_RANK']      = $member['rank'];


        if($member['rank']=='administrator'){
        header("location: login_reg.php");
        }

        else if($member['rank']=='student'){
        header("location: student.php");
        }
        else if($member['rank']=='candidate'){
        header("location: candidate.php");
        }

        }else{
        print "Incorrect username or password";

            session_write_close();

Answer 1

$sql = "SELECT a.login_id,a.username,a.password,a.rank,b.status FROM login2 as a INNER JOIN login_stat2 as b ON a.login_id = b.login_id WHERE a.username     ='".$username."' AND a.password='".$pass."' AND b.status='ACTIVE'";

$result = mysqli_query($con,$sql)or die(mysqli_error($con));

if(mysqli_num_rows($result)) {
   echo 'Login success';
} else {
   echo 'invalid username and password';
}

The mysqli_num_rows() function returns the number of rows in a result set.

Updated Code

//create connection
$conn = new mysqli('localhost', 'root', '', 'demo');

//check connection
if($conn->connect_error) {
  die("connection failed: ".$conn->connect_error);
}
echo "Connection Successful <br>";

$sql = "SELECT a.login_id,a.username,a.password,a.rank,b.status FROM login2 as a INNER JOIN login_stat2 as b ON a.login_id = b.login_id WHERE a.username ='admin' AND a.password='admin' AND b.status='ACTIVE'";

$result = mysqli_query($conn,$sql) or die(mysqli_error($con));
if(mysqli_num_rows($result)) {
    echo "login";
} else {
    print "Incorrect username or password";
}