NULL and COALESCE in SQL
SQL interview exercise on Select & Filter, difficulty 2 of 3. Solve it in the editor beside a worked example; the tests run the moment you do.
Return every customer with a contact column: their email, or the text 'no email' when there is none. Columns: name, contact. Sorted by name.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Progress is saved in your browser, and in your account if you sign in.