人太菜，求改错解决思路

//数据库查询相关
function sqlUserInfo($username, $password)
{
    $users = trim($username);
    $pass = trim($password);

    $conn=mysql_connect($host,$users,$passwords);
    mysql_select_db($database,$conn);
    //echo "start connect db";
    if(!$db)
        return false;
    //echo "start query db";

    $query = "SELECT * FROM tb_users WHERE username = '".$users."' AND password = '".$pass."'";
    $sql = mysql_query($query, $conn) or die(mysql_error());

    if(mysql_num_rows($sql) == 1)
        return true;
    else
        die("数据库查询失败！");
    return false;
}