SQL/PHP "WHERE" not returning correct value? -

the code display returned values , and if greater 1 return "yes". having trouble clause in $check. when take out code works fine when add it, page returns incorrect values. ideas what's wrong?

<?php  $con = mysqli_connect("127.0.0.1","root","","lian");  $u= $_get['username']; $pw = $_get['password'];  $check = "select username,password users username='$u' , password='$pw'";  $login = mysqli_query($con,$check) or die(mysqli_error($con));  $num_rows = mysqli_num_rows($login); echo "$num_rows \n";  if (mysqli_num_rows($login) == 1) { $row = mysqli_fetch_assoc($login); echo 'yes';  exit; }  else { echo 'no'; exit; } 

leaving aside injection vulnerabilities, may because of special characters or whitespace. try trim'ing values.

$u = trim($_get['username']); $pwd = trim($_get['password']); 

are getting number of results 0? try echoing statement in development environment check statement is.