$SQL UPDATE doesn't work when added WHERE CLAUSE - mysql

Question

I know I am simply missing the simplest thing here but cant seem to figure it out.
so this works with this code but changes all rows of the database as opposed to just the one with the page id...
<? $pageid= $_GET["id"];
$sql = "SELECT id, first_name, last_name, email, bio, job, job2, job3 FROM `".weapons."` WHERE id = $pageid";
if(isset($_POST['Update']))
{
$first_name = $_POST['first_name'];
$last_name = $_POST['last_name'];
$job = $_POST['job'];
$job2 = $_POST['job2'];
$job3 = $_POST['job3'];
$bio = $_POST['bio'];
$email = $_POST['email'];
$sql = "UPDATE weapons SET first_name='$first_name', email='$email' , job='$job', job2='$job2', job3='$job3', bio='$bio', last_name='$last_name'";
if (#mysql_query($sql)) {
echo('<p>Update Complete</p>');
} else {
echo('<p>Error updating: ' . mysql_error() . '</p>');
}
}else{ ...
however when adding the WHERE clause, like as follows
$sql = "UPDATE weapons SET first_name='$first_name', email='$email' , job='$job', job2='$job2', job3='$job3', bio='$bio', last_name='$last_name' WHERE id = $pageid";
I get an error
Error updating: 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 '' at line 1
Any help would be great, thanks
EDIT
I actually missed a super easy thing, which is what I initially assumed, I had at first in my form had <form method='post' enctype='multipart/form-data' action='submit.php'> however that obviously messed up the get id because there isnt an idea, so even if that page was submit.php?id=4 when you hit submit it wouldnt run because the id would be gone.
Switching the code to <form method='post' enctype='multipart/form-data' action='#'> did just the trick.
Thanks for the help guys and I am looking into the sql injection now and working on how to better secure my site.

Answer 1

Please escape your strings before you create your SQL statement. Various characters in your input values will both break your query and open a HUGE security hole. That may very well be your problem. Look at this post for more info How can I prevent SQL injection in PHP?
In short, you assignments would look like this:
$first_name = mysql_real_escape_string($_POST['first_name']);
echo $sql; before you run it and post what that outputs.