I might be a newb for asking this or i'm just overthinking

i have a rating system wheere when someboy rates it grabs the number from the db, do the math and then update the number in the row

if two people happen to click rate at the same time.. wouldn't that cause problems or chances of that happen is like winning the lottary

If you're pulling a value from the database and then updating it in a separate query there is a chance that the value will be modified by a separate process between the select and update queries.

A way to avoid this would be to have the database "do the math" instead of PHP. Depending on how you are storing and calculating you may be able to do it with an update query, or you may have to use a stored procedure.