COUNT(DISTINCT ...) in SQL
SQL interview exercise on Aggregation, difficulty 2 of 3. Solve it in the editor beside a worked example, or cold in Interview mode with the example hidden; the tests run the moment you do.
For each order status return the number of orders and the number of different customers who placed them. Columns: status, orders, customers. Sorted by status.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Interview mode hides the example: solve it from memory, without the hint or the solution, and it counts as solved cold. Progress is saved in your browser, and in your account if you sign in.