SQL queries

A. Find the number of customers who are signed up for at least one type of communication.

B. List the number of customers who are signed up for each communication name.

C. List the names and addresses of customers who have both CHECKING and SAVINGS accounts.

D. List the customer.id of customers who do not have any active bank accounts.

E. Sign up a customer (id=47) for SMS_ALERT by inserting a new row in communication_channel.