Question 8735 – SQL

Consider the following relational schema:

  employee(empId, empName, empDept)
  customer(custId, custName, salesRepId, rating)

salesRepId is a foreign key referring to empId of the employee relation. Assume that each employee makes a sale to at least one customer. What does the following query return?

SELECT empName
        FROM employee E
        WHERE NOT EXISTS (SELECT custId
                         FROM customer C
                         WHERE C.salesRepId = E.empId
                         AND C.rating <> `GOOD`); 

Correct Answer: D

The inner query i.e., ② represents all customers having other than ‘GOOD’ while the entire query represents name of all employees with all their customers having a ‘good rating’.