สอบถามเกียวกับฐานข้อมุล MySQL หน่อยครับ ขอบคุณครับ

$sql = "select NULLIF( t1.simple_test_one,  t2.simple_test_two) as result from db_test_1 t1,  db_test_2 t2";
$res = mysqli_query($link,$sql) or die(mysqli_error());
$data = mysqli_fetch_assoc($res);
if(is_null($data["result"])){
      echo "yes";
}else {
     echo "no";
}

$sql = "select NULLIF( t1.simple_test_one,  t2.simple_test_two) as result from db_test_1 t1,  db_test_2 t2";
$res = mysql_query($sql) or die(mysql_error());
$data = mysql_fetch_assoc($res);
if(is_null($data["result"])){
      echo "yes";
}else {
     echo "no";
}