LeetCode（数据库）- Hopper Company Queries III

WITH RECURSIVE cal AS(
    SELECT 1 l, 1 mon1, 2 mon2, 3 mon3
    UNION ALL
    SELECT l + 1, mon1 + 1, mon1 + 2, mon1 + 3 FROM cal WHERE mon1 < 10
),
t AS(SELECT a.ride_id, ride_distance, ride_duration, requested_at FROM Rides r JOIN AcceptedRides a ON r.ride_id = a.ride_id AND requested_at BETWEEN '2020-01-01' AND '2020-12-31')
SELECT l month, IFNULL(ROUND(SUM(ride_distance) / 3, 2), 0) average_ride_distance, IFNULL(ROUND(SUM(ride_duration) / 3, 2), 0) average_ride_duration
FROM cal LEFT JOIN t ON MONTH(requested_at) IN (mon1, mon2, mon3)
GROUP BY l