Call to undefined function mysql_query() with Login [duplicate]

Answer 1

You are mixing mysql and mysqli

Change these lines:

$sql = mysql_query("SELECT * FROM login WHERE username = '".$_POST['username']."' and password = '".md5($_POST['password'])."'");
$row = mysql_num_rows($sql);

to

$sql = mysqli_query($success, "SELECT * FROM login WHERE username = '".$_POST['username']."' and password = '".md5($_POST['password'])."'");
$row = mysqli_num_rows($sql);