SQL Query Needed

It goes something like this... a member signs up and enters in the [login to view URL] address of their spouse into a field. Then once they register, a query is automatically run and checks if that [login to view URL] address already exists and if it does, then it changes that found [login to view URL] address's membership plan value from 1 to 2. What I need is a query that will: Search for a matching [login to view URL] address from column A from table A and column C from table A and if it exists, then set value of field plan_type in table B from 1 to 2. And each row/user in the table has their own unique ID. So something like if the [login to view URL] address exists in column C from table A because it's been entered during registration in column A from table A, then set that found [login to view URL] address in column C from table A's user plan which is in a different table (table B) from 1 to 2.