GATE CS 2014 Set 3 — Question 64

MCQ+2 / -0.67MediumSubqueriesSQLDatabases

Databases → SQL → Subqueries

Last updated 5 September 2026

Question

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) Names of all the employees with all their customers having a ‘GOOD’ rating. Solution The SQL query selects empName from the employee table where a certain condition holds. The condition is WHERE NOT EXISTS (...) . The subquery selects customers associated with the employee (C.salesRepId = E.empId) who have a rating that is not'GOOD' (C.rating <> 'GOOD'). So, NOT EXISTS returns TRUE if there are no customers for that employee with a rating other than 'GOOD'. In other words, the set of customers with 'BAD' (or any non-GOOD) rating is empty. This implies that all customers associated with the employee must have a rating of 'GOOD'. Since the problem statement assumes each employee makes a sale to at least one customer, we don't need to worry about employees with zero customers (for whom the condition would also be vacuously true). Therefore, the query returns the names of employees where all their customers have a 'GOOD' rating. Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer (D) Names of all the employees with all their customers having a ‘GOOD’ rating. Solution The SQL query selects empName from the employee table where a certain condition holds. The condition is WHERE NOT EXISTS (...) . The subquery selects customers associated with the employee (C.salesRepId = E.empId) who have a rating that is not'GOOD' (C.rating <> 'GOOD'). So, NOT EXISTS returns TRUE if there are no customers for that employee with a rating other than 'GOOD'. In other words, the set of customers with 'BAD' (or any non-GOOD) rating is empty. This implies that all customers associated with the employee must have a rating of 'GOOD'. Since the problem statement assumes each employee makes a sale to at least one customer, we don't need to worry about employees with zero customers (for whom the condition would also be vacuously true). Therefore, the query returns the names of employees where all their customers have a 'GOOD' rating.

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