Days on which an outlet was open but took in no bill (a recursive CTE).   [3 row(s)]
outlet | empty_days | first      | last
-------+------------+------------+-----------
O01    | 8          | 2025-11-06 | 2026-09-15
O02    | 38         | 2025-10-01 | 2026-09-23
O03    | 23         | 2026-01-12 | 2026-09-15

