Strange row count problem

[S3NTIN3L]

I am making a favourite option for a dating site.
I am trying to make the option 'delete' if you already have that fav or 'add' if you dont.
So I do a query based on the users id to see if they are a fav - problem is the code only works for some favs and not others.
Please check it out:

				<?php				
					if(isset($_GET['id']))
					{
						$id = $_GET['id'];
						$user_id = $_SESSION['SESS_MEMBER_ID'];

					echo "<a href='chat.php'>Chat</a>&nbsp;";	

					$qry = "SELECT id FROM favourites WHERE favourite_id = '$id' AND id = $user_id";
					$result = mysql_query($qry);

					if(mysql_num_rows($result) > 0)
					{
						echo "<a href='delete-favourite-exec.php?id=$id'>Delete from favourites</a>";
					}
					else
					{
						echo "<a href='favourite-exec.php?id=$id'>Add to favourites</a>";
					}
			?>	

[sandthipe]

without knowing more about your DB setup, it's hard to guess what might be wrong. but my first thought is that you may double-check the indexes on your 'favourites' table. probably the 'id' field should be the primary key and the 'favourite_id' field should be a simple index. make sure the 'favourite_id' field is not a UNIQUE index, as that would mess things up

[S3NTIN3L]

I think its sorted now - I removed the primary key so there are no primary keys now at all.
Seems to have worked - cheers for the help anyway.