Conditional aggregation 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 category return how many products are in stock (stock above 0) and how many are out of stock. Every category appears, even with a 0. Columns: category, in_stock, out_of_stock. Sorted by category.
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.