# Measure Customers Ordering from Bottom-Quartile Restaurants Write one PostgreSQL SELECT statement or CTE query. Do not create, alter, or modify tables. ## Schema delivery_orders | column | type | |---|---| | delivery_id | integer | | order_place_time | timestamp | | restaurant_id | integer | | customer_id | integer | order_value | column | type | |---|---| | delivery_id | integer | | order_total | real | ## Data Guarantees - `delivery_orders.delivery_id` is unique, and every 2021 delivery has exactly one matching row in `order_value`. - `order_place_time`, `restaurant_id`, `customer_id`, and `order_total` are non-NULL for those matched deliveries. - Every calendar month in 2021 has at least one matched delivery. ## Task Use deliveries placed on or after `2021-01-01` and before `2022-01-01`. For each calendar month: 1. Cast each matched `order_total` to `numeric` before aggregation, then sum those numeric values by restaurant to calculate each restaurant's monthly sales. Use these numeric sums when assigning sales buckets. 2. Assign the restaurants that had at least one matched delivery that month to four sales buckets with `NTILE(4)`, ordered by monthly sales ascending and then by `restaurant_id` ascending for deterministic ties. 3. Count all distinct customers with a matched delivery that month. 4. Count the distinct customers who placed at least one order from a restaurant assigned to bucket 1 that month. ## Required Output Return exactly these columns: | column | meaning | |---|---| | `order_month` | The first date of the calendar month, as a date | | `bottom_quartile_customer_pct` | `100 *` the number of distinct customers with at least one bucket-1 order that month, divided by all distinct customers with a matched delivery that month, rounded to two decimal places and returned as `numeric(5,2)` | Return exactly 12 rows, one for each month of 2021, sorted by `order_month` ascending. ## Constraints - A customer who orders from several bucket-1 restaurants counts once in the numerator. - A customer who orders from both bucket-1 and other restaurants still counts once in the numerator and once in the denominator. - Use the restaurant-ID tie-break when assigning buckets; do not rank restaurants by individual order values.