You need one table, for all participants, donors and volunteers. a field in this table can identify which is which and you will need to consider the fact that one individual may be a member of more than one of these categories. How you implement that depends on the needs of the rest of your database. A check box field with a check box for each category is one option. Another option is to use a related table where you add one related record for each category to which that "customer" belongs.