php/mySQL error: mysql_num_rows(): supplied argument is not a valid MySQL result

I'm trying to INSERT INTO a mySQL database and I'm getting this error on:

if (mysql_num_rows(开发者_运维问答$login) == 1){

Here is the php, The php does add the user to the database. I can't figure it out.

<?
session_start();
require("config.php");

$u = $_GET['username'];
$pw = $_GET['password'];
$pwh = $_GET['passwordhint'];
$em = $_GET['email'];
$zc = $_GET['zipcode'];


$check = "INSERT INTO family (loginName, email, password, passwordhint, location) VALUES ('$u', '$pw', '$pwh', '$em', '$zc')";


$login = mysql_query($check, $link) or die(mysql_error());


if (mysql_num_rows($login) == 1) {
$row = mysql_fetch_assoc($login);
echo 'Yes';exit;


} else {
echo 'No';exit;
}

mysql_close($link);
?>

Thanks,

You're doing an INSERT query, so $login won't contain any result set, it's either true or false.

So instead of this:

if (mysql_num_rows($login) == 1) {

You can either do this:

if (mysql_affected_rows($link) == 1) {

Or this:

if ($login == true) {

Also, you don't need this line anymore:

$row = mysql_fetch_assoc($login);

Unrelated to your question, but a very important thing to remember when doing SQL queries: you'll need to escape all your $_GET data with mysql_real_escape_string() just before inserting, so as to prevent SQL injection.

mysql_query() returns True/False for INSERT, UPDATE, DELETE, DROP...