Find the names of customers who have a mortgage loan.
select t1.cust_name from customer as t1 join loan as t2 on t1.cust_id = t2.cust_id where t2.loan_type = 'Mortgages'
who are those who do not have a mortgage?
select cust_name from customer except select t1.cust_name from customer as t1 join loan as t2 on t1.cust_id = t2.cust_id where t2.loan_type = 'Mortgages'