为什么我的查询从不正确编辑MySQL表的成员？

I am creating a basic members only website, and one of my pages is meant to edit a user's information from an admin view. It accesses the the database named contacts, and then the table tblUsers, but somewhere along the line when it finally goes to edit the info it doesn't save.

<?php 
include("main.php");

connectDB();

//check for submit being pressed
if(isset($_POST['submit']))
{   //check for empty fields
    if($_POST['fName']!="" && $_POST['lName']!="" && $_POST['uName']!="" && $_POST['email']!="" && $_POST['address']!="" && $_POST['city']!="" && $_POST['state']!="" && $_POST['zip']!="" && $_POST['phone']!="" && $_POST['signup']!="")
    {
        $SQL="Update tblUsers SET firstName='".$_POST['fName']."', lastName='".$_POST['lName']."',userName='".$_POST['uName']."', email='".$_POST['email']."', address='".$_POST['address']."', city='".$_POST['city']."', state='".$_POST['state']."', zip='".$_POST['zip']."', phone='".$_POST['phone']."', signupDate='".$_POST['signup']."' WHERE userID=".$_POST['userID'];

        $response=mysql_query($SQL);
        //redirect with status update
        header("Location:editMember.php?id=".$_POST['userID']."&status=1");
    }
    else
    {   //redirect with status update
        header("Location:editMember.php?id=".$_POST['userID']."&status=2");
    }

}

//check for ID, if none redirect
if($_GET['id']=="")
{
    header("Location:adminView.php");
    exit;
}


//function to display form
function displayForm($strMessage, $userid, $response="")
{
    echo    "<center><strong>" . $strMessage . "</strong></center><br><br>";
    echo    "<form method=\"post\" action=\"" . $_SERVER['PHP_SELF'] . "\">
";
    echo    "<table>
";
    echo    "<tr>
";
    echo        "<td>
";
    echo            "First Name: <input type=\"text\" name=\"fName\" value=\"" . mysql_result($response,0,"firstName") . "\">
";
    echo        "</td>
";
            "</tr>
";
    echo    "<tr>
";
    echo        "<td>
";
    echo            "Last Name: <input type=\"text\" name=\"lName\" value=\"" . mysql_result($response,0,"lastName") . "\">
";
    echo        "</td>
";
            "</tr>
";
    echo    "<tr>
";
    echo        "<td>
";
    echo            "Username: <input type=\"text\" name=\"uName\" value=\"" . mysql_result($response,0,"username") . "\">
";
    echo        "</td>
";
            "</tr>
";
    echo    "<tr>
";
    echo        "<td>
";
    echo            "Email: <input type=\"text\" name=\"email\" value=\"" . mysql_result($response,0,"email") . "\">
";
    echo        "</td>
";
    echo    "</tr>
";
    echo    "<tr>
";
    echo        "<td>
";
    echo            "Address: <input type=\"text\" name=\"address\" value=\"" . mysql_result($response,0,"address") . "\">
";
    echo        "</td>
";
            "</tr>
";
    echo    "<tr>
";
    echo        "<td>
";
    echo            "City: <input type=\"text\" name=\"city\" value=\"" . mysql_result($response,0,"city") . "\">
";
    echo        "</td>
";
            "</tr>
";
    echo    "<tr>
";
    echo        "<td>
";
    echo            "State: <input type=\"text\" name=\"state\" value=\"" . mysql_result($response,0,"state") . "\">
";
    echo        "</td>
";
            "</tr>
";
    echo    "<tr>
";
    echo        "<td>
";
    echo            "Zip: <input type=\"text\" name=\"zip\" value=\"" . mysql_result($response,0,"zip") . "\">
";
    echo        "</td>
";
            "</tr>
";
    echo    "<tr>
";
    echo        "<td>
";
    echo            "Phone Number: <input type=\"text\" name=\"phone\" value=\"" . mysql_result($response,0,"phone") . "\">
";
    echo        "</td>
";
            "</tr>
";
    echo    "<tr>
";
    echo        "<td>
";
    echo            "Sign-up Date: <input type=\"text\" name=\"signup\" value=\"" . mysql_result($response,0,"signupDate") . "\">
";
    echo        "</td>
";
            "</tr>
";
    echo    "<tr>
";
    echo        "<td>
";
    echo            "<center><input type=\"submit\" value=\"submit\" name=\"submit\"/></center>
";
    echo        "</td>
";
    echo    "</tr>
";
    echo    "</table>
";
    echo    "</form>
";
}
//status switch to show message if successful edit
switch($_GET['status'])
{
    case 1:
    $strMessage="Changes have been saved";
    break;

    case 2:
    $strMessage="All fields are required.";
    break;

    default:
    $strMessage="Edit users.";
}
//query to show details of a user with specified userID
$SQL="SELECT * FROM tblusers WHERE userid=".$_GET['id'];
$response=mysql_query($SQL);

if($response && mysql_num_rows($response) > 0)
{
    displayForm($strMessage,$_GET['id'],$response);
}
else
{
    header("Location:adminView.php");
}
?>

<html>
        <style type="text/css">
            table {border: 1px solid black; margin-left:auto; 
                        margin-right:auto;}
            tr {border: 1px solid black}
            td {border: 1px solid black;}
            body {background-color: orange;}
            *{font-family:Arial;}
        </style>
<body>
</body>
</html>

userID was looking for a posted value, but was never being posted in the form so nothing happened, question answered.