ระบบ Login ผม ID ถูก Password ถูก แต่มัน Loginไม่ได้ ทำไมครับ?

function loginchk()
{
	
	$username=$_POST["username"];
	$password=$_POST["password"];
	if($username==NULL||$username=="/")
	{
	return 0;
	}
	$conn = mysql_connect($host, $user, $pw)or die("Can't Connect Database Server");
	$command="SELECT password FROM account WHERE username='$username'";
	$tmp1 = mysql_query($command, $conn)or die("Can't get Password infomation");
	$cttmp2=mysql_fetch_array($tmp1);
	
	if($cttmp2[0]==$password)
	{
		return 1;
	}
	else
	{
		return 0;
	}	
	mysql_close;
}