Use string to update database

I have a form that has multple fields created dynamically based on a count so they all have the same name. When I look at the data parsed through I see that I have a string... 1,2,3,4,5, etc. Never more than 10 or so.

I need to update one field in a temp table in MySql (which already has the same number of records as the string has numbers) from this string and don't really need it to do more than propogate the next record that has a current value of either zero or null.

Does anyone have an example of a loop/query for this?, not finding much help in the books.

Thanks!