Hello, how many complaints have we had?
select count ( * ) from complaints
How about customers?
select count ( * ) from customers
How many customers have filed complaints?
select count ( * ) from customers where customer_id in ( select customer_id from complaints )
And how many have not filed complaints?
select count ( * ) from customers where customer_id not in ( select customer_id from complaints )
What is that customer's phone number?
select phone_number from customers where customer_id not in ( select customer_id from complaints )
what about that customer's email?
select email_address from customers where customer_id not in ( select customer_id from complaints )