check username script.... times 2

php/mysql

i prefer non theoretical answers.

here is the block of code that dreamweaver has entered for over 5 years now to "check username"

// *** Redirect if username exists

$MM_flag="MM_insert";

if (isset($_POST[$MM_flag])) {

  $MM_dupKeyRedirect="redirecturl.php";

  $loginUsername = $_POST['username'];

  $LoginRS__query = sprintf("SELECT username FROM database WHERE username=%s", GetSQLValueString($loginUsername, "text"));

  mysql_select_db($database_123, $123);

  $LoginRS=mysql_query($LoginRS__query, $123) or die(mysql_error());

  $loginFoundUser = mysql_num_rows($LoginRS);

  //if there is a row in the database, the username was found - can not add the requested username

  if($loginFoundUser){

    $MM_qsChar = "?";

    //append the username to the redirect page

    if (substr_count($MM_dupKeyRedirect,"?") >=1) $MM_qsChar = "&";

    $MM_dupKeyRedirect = $MM_dupKeyRedirect . $MM_qsChar ."requsername=".$loginUsername;

    header ("Location: $MM_dupKeyRedirect");

    exit;

  }

}

converting that to check multiple items.

and if this block of default code is garbage, a better suited way to do this.  each item needs to have it's own check, and own trigger, and own resulting error message for users identified, preferably without using a url redirect to avoid the use of url parameters if possible.  thanks in advance.