Days between two dates in SQL
SQL interview exercise on Strings, Dates & CASE, 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 customer who has ordered, return how many days passed between joining and their first order, as a whole number. Columns: customer, days_to_first_order. Fewest days first, then by customer.
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.