Beginner
#001
Find users older than 20
Write a SQL query to find users whose age is greater than 20.
Problem index
Browse every SQL practice problem.
Each problem has a crawlable detail page with schema, sample data, expected output, answer, explanation, common mistakes, and related concepts.
All problems
26 crawlable SQL problem pages
Use this index when you want a direct link to a specific problem page.
Beginner
#002
Select product names and prices
Return only the product name and price columns from the products table.
Beginner
#003
Show newest orders first
List all orders so the most recent order appears first.
Intermediate
#004
Count orders per customer
Return each customer_id and the number of orders placed by that customer.
Intermediate
#005
List customers with their orders
Return the customer name, order id, and total amount for orders that have a matching customer.
Intermediate
#006
Find orders above the average amount
Return orders whose total amount is greater than the average order amount.
Intermediate
#007
Average salary by department
Calculate the average salary for each department.
Beginner
#008
Find employees without a manager
Return employees whose manager_id is NULL.
Advanced
#009
Filter grouped results with HAVING
Find customer_id values that have placed at least two orders.
Intermediate
#010
Label orders with CASE
Return each order id and a size label: High for orders of 100 or more, otherwise Standard.
Beginner
#011
List unique product categories
Return each product category only once from the products table.
Intermediate
#012
Find orders placed in January 2019
Return orders created during January 2019 using a range condition.
Beginner
#013
Show the two most expensive products
Return the two products with the highest price.
Beginner
#014
Count orders that used a discount
Return the number of orders whose discount amount is greater than zero.
Intermediate
#015
Find categories with average price at least 50
Return product categories whose average price is at least 50.
Intermediate
#016
List emails of customers who ordered Gizmo products
Return each customer email once for customers who ordered at least one product in the Gizmo category.
Intermediate
#017
Find customers with no orders
Return customers who do not have any matching rows in the orders table.
Intermediate
#018
Find products that were never ordered
Return product titles for products that do not appear in any order.
Intermediate
#019
Find students enrolled in at least one course
Return student names for students who appear in the enrollments table.
Beginner
#020
Show a fallback display name
Return each user's id and display name. Use nickname when it exists, otherwise use name.
Advanced
#021
Rank orders within each customer
Return each order with a rank number based on total_amount from highest to lowest within the same customer.
Intermediate
#022
Combine email lists without duplicates
Return a single list of email addresses from customers and newsletter_signups without duplicates.
Intermediate
#023
Find duplicate customer emails
Return email values that appear more than once in the customers table.
Intermediate
#024
Find each employee's manager name
Return each employee name with the name of their manager, keeping employees who have no manager.
Advanced
#025
Find the second highest salary
Return the highest salary that is lower than the overall highest salary.
Advanced
#026
Find the top product in each category
Return the highest priced product for each category.