$sql_server = "localhost";      //sqlserver url
$sql_server_usr = "sqlserver_username";
$sql_server_pas = "sqlserver_password";

$mysql = mysql_connect($sql_server, $sql_server_usr, $sql_server_pas) or die("couldn't connect to server");
mysql_select_db("sql_database", $mysql) or die("couldn't select the database");

$check = mysql_query('SELECT * FROM table_name WHERE username_column = '."'".$username."'") or die("couldn't check the query");
$info = mysql_fetch_array($check); //or die("couldn't get the array");

$sql_str_username = $regOptions["username"];

if ($req_username == $sql_str_username)
{
    echo '<script type="text/javascript">
            alert("Username or email already exist!")
                    </script>';
}
else
{
    $req_username = $regOptions["username"];
    $req_password = $regOptions["password"];
    $req_email = $regOptions['email'];
    mysql_query('INSERT INTO Users(username_column, password_column) VALUES '."('".$req_username."', '".$req_password."'");

};
mysql_close($mysql) or die("couldn't close server");