updatin query problem

[hellz]

hi, im trying to get my stock field in my database to decrease when a user buys an item and they select the quantity. The current code im using is

 $quantity = $_POST['quantity'];
		$sql = "Update item SET Stock = Stock - $quantity WHERE ProductId = $ProductId";
		$result = mysql_query($sql) or die ( mysql_error() );

Any Help?

[devinemke]

and what exactly is the problem?

[hellz]

the above code doesn't work and gives me an error:

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 'WHERE ProductId =' at line 1

I dont know how to fix it.

[dagon]

is $ProductId defined?

[hellz]

yea that was the problem, it was id not productid lol thanks for help