Join, then aggregate in SQL
SQL interview exercise on Joins, 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.
Return the total value of each order: the sum of quantity × unit_price over its lines. Use the unit_price on the order line, which is what was actually charged, not the product's current price. Columns: order_id, ordered_on, total. Sorted by order_id.
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.