when running the below code, I do get what i want from the database, and result on the page, but also i'm receiving error message:

warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in C:\Documents and Settings\surplape\Desktop\xampplite\htdocs\drupal\includes\common.inc(1695) : eval()'d code on line 17.

when I replace $result = mysql_query($query) with $result = mysql_query($query) or die (mysql_error())

I get

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'AND uid = 1' at line 1

but syntax seems fine to me, any ideas?

the code:

//get node id
if (arg(0) == 'node' && is_numeric(arg(1))) $nodeid = arg(1);

//get user id
global $user;

$query= "SELECT * FROM webform_submissions WHERE nid = $nid AND uid = $user->uid";
$result = mysql_query($query);
$row = mysql_num_rows($result);
if ($row > 0)
{
echo "bravo you answered already!";
}