Exam 7: Subqueries & Set Operations
Difficulty: Intermediate
Topics covered: Subqueries in WHERE, EXISTS, NOT EXISTS, UNION
Each question shows the target output. Write a SQL query that produces exactly those columns and rows.
Question 1
Find all customers who have placed at least one order. Use a subquery with IN. Return all columns from customers.
Question 2
Find all products that have never appeared in a completed order. Use NOT IN. Return all columns from products.
Question 3
Find all customers who have placed at least one completed order. Use EXISTS. Return customer_id and name.
Question 4
Find all completed orders where total_amount is above the average total_amount of all completed orders. Return all columns from orders.
Question 5
Use UNION to produce a single list of all customer_id values from the customers table combined with the distinct customer_id values from the orders table. Return a single column named customer_id.