PHP javascript表单证验未通过而表单依然提交

PHP javascript表单验证未通过而表单依然提交
如题，我的情况是不输入任何数据，点击提交注册，会弹出“请输入用户名”这样的提示，点击确定后 就转到另一个页面，并只显示一句话：Column 'UserName' cannot be null。
下面是代码：

HTML code

<!--

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--><?php require_once('Connections/conetion.php'); ?><?php function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "") 
{
  $theValue = (!get_magic_quotes_gpc()) ? addslashes($theValue) : $theValue;

  switch ($theType) {
    case "text":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;    
    case "long":
    case "int":
      $theValue = ($theValue != "") ? intval($theValue) : "NULL";
      break;
    case "double":
      $theValue = ($theValue != "") ? "'" . doubleval($theValue) . "'" : "NULL";
      break;
    case "date":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "defined":
      $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;
      break;
  }
  return $theValue;
}

$editFormAction = $_SERVER['PHP_SELF'];
if (isset($_SERVER['QUERY_STRING'])) {
  $editFormAction .= "?" . htmlentities($_SERVER['QUERY_STRING']);
}

if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "form1")) {
  $insertSQL = sprintf("INSERT INTO member (UserName, Password, Email) VALUES (%s, %s, %s)",
                       GetSQLValueString($_POST['UserName'], "text"),
                       GetSQLValueString($_POST['Password'], "text"),
                       GetSQLValueString($_POST['Email'], "text"));

  mysql_select_db($database_conetion, $conetion);
  $Result1 = mysql_query($insertSQL, $conetion) or die(mysql_error());

  $insertGoTo = "index.php";
  if (isset($_SERVER['QUERY_STRING'])) {
    $insertGoTo .= (strpos($insertGoTo, '?')) ? "&" : "?";
    $insertGoTo .= $_SERVER['QUERY_STRING'];
  }
  header(sprintf("Location: %s", $insertGoTo));
}
?><meta http-equiv="Content-Type" content="text/html; charset=gb2312"><title></title>

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