I take it this is the same thread as before referring to the SQL query - although I have no idea why you have just created a new thread for your reply - this could get confusing....
The purpose of -1 might be where any positive number is a valid value. i.e. 0 is a valid response. In this case it may be argued that NULL could be just as helpful, but PHP doesn't seem to distinguish between 0 and NULL when you pull out a recordset, therefore checking for a negative number is one of the easiest ways to do it.
