Hopper Company Queries I Problem

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+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| driver_id   | int     |
| join_date   | date    |
+-------------+---------+
driver_id is the primary key for this table.
Each row of this table contains the driver's ID and the date they joined the Hopper company.

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+--------------+---------+
| Column Name  | Type    |
+--------------+---------+
| ride_id      | int     |
| user_id      | int     |
| requested_at | date    |
+--------------+---------+
ride_id is the primary key for this table.
Each row of this table contains the ID of a ride, the user's ID that requested it, and the day they requested it.
There may be some ride requests in this table that were not accepted.

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+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| ride_id       | int     |
| driver_id     | int     |
| ride_distance | int     |
| ride_duration | int     |
+---------------+---------+
ride_id is the primary key for this table.
Each row of this table contains some information about an accepted ride.
It is guaranteed that each accepted ride exists in the Rides table.

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Drivers table:
+-----------+------------+
| driver_id | join_date  |
+-----------+------------+
| 10        | 2019-12-10 |
| 8         | 2020-1-13  |
| 5         | 2020-2-16  |
| 7         | 2020-3-8   |
| 4         | 2020-5-17  |
| 1         | 2020-10-24 |
| 6         | 2021-1-5   |
+-----------+------------+

Rides table:
+---------+---------+--------------+
| ride_id | user_id | requested_at |
+---------+---------+--------------+
| 6       | 75      | 2019-12-9    |
| 1       | 54      | 2020-2-9     |
| 10      | 63      | 2020-3-4     |
| 19      | 39      | 2020-4-6     |
| 3       | 41      | 2020-6-3     |
| 13      | 52      | 2020-6-22    |
| 7       | 69      | 2020-7-16    |
| 17      | 70      | 2020-8-25    |
| 20      | 81      | 2020-11-2    |
| 5       | 57      | 2020-11-9    |
| 2       | 42      | 2020-12-9    |
| 11      | 68      | 2021-1-11    |
| 15      | 32      | 2021-1-17    |
| 12      | 11      | 2021-1-19    |
| 14      | 18      | 2021-1-27    |
+---------+---------+--------------+

AcceptedRides table:
+---------+-----------+---------------+---------------+
| ride_id | driver_id | ride_distance | ride_duration |
+---------+-----------+---------------+---------------+
| 10      | 10        | 63            | 38            |
| 13      | 10        | 73            | 96            |
| 7       | 8         | 100           | 28            |
| 17      | 7         | 119           | 68            |
| 20      | 1         | 121           | 92            |
| 5       | 7         | 42            | 101           |
| 2       | 4         | 6             | 38            |
| 11      | 8         | 37            | 43            |
| 15      | 8         | 108           | 82            |
| 12      | 8         | 38            | 34            |
| 14      | 1         | 90            | 74            |
+---------+-----------+---------------+---------------+

Result table:
+-------+----------------+----------------+
| month | active_drivers | accepted_rides |
+-------+----------------+----------------+
| 1     | 2              | 0              |
| 2     | 3              | 0              |
| 3     | 4              | 1              |
| 4     | 4              | 0              |
| 5     | 5              | 0              |
| 6     | 5              | 1              |
| 7     | 5              | 1              |
| 8     | 5              | 1              |
| 9     | 5              | 0              |
| 10    | 6              | 0              |
| 11    | 6              | 2              |
| 12    | 6              | 1              |
+-------+----------------+----------------+

By the end of January --> two active drivers (10, 8) and no accepted rides.
By the end of February --> three active drivers (10, 8, 5) and no accepted rides.
By the end of March --> four active drivers (10, 8, 5, 7) and one accepted ride (10).
By the end of April --> four active drivers (10, 8, 5, 7) and no accepted rides.
By the end of May --> five active drivers (10, 8, 5, 7, 4) and no accepted rides.
By the end of June --> five active drivers (10, 8, 5, 7, 4) and one accepted ride (13).
By the end of July --> five active drivers (10, 8, 5, 7, 4) and one accepted ride (7).
By the end of August --> five active drivers (10, 8, 5, 7, 4) and one accepted ride (17).
By the end of Septemeber --> five active drivers (10, 8, 5, 7, 4) and no accepted rides.
By the end of October --> six active drivers (10, 8, 5, 7, 4, 1) and no accepted rides.
By the end of November --> six active drivers (10, 8, 5, 7, 4, 1) and two accepted rides (20, 5).
By the end of December --> six active drivers (10, 8, 5, 7, 4, 1) and one accepted ride (2).

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select t.month, 
    count(distinct driver_id) active_drivers,
    count(distinct rides.ride_id) accepted_rides 
from
    ((select 1 as month)
    union (select 2 as month)
    union (select 3 as month)
    union (select 4 as month)
    union (select 5 as month)
    union (select 6 as month)
    union (select 7 as month)
    union (select 8 as month)
    union (select 9 as month)
    union (select 10 as month)
    union (select 11 as month)
    union (select 12 as month)) t
left join
    (select driver_id, 
    (case when year(join_date) = 2019 then '1' else month(join_date) end) `month`
    from Drivers 
    where year(join_date) <= 2020) d
on d.month <= t.month
left join
    (select month(requested_at) as `month`, a.ride_id
    from AcceptedRides a 
    join Rides r
    on r.ride_id = a.ride_id
    where year(requested_at) = 2020) rides
on t.month = rides.month
group by t.month 
order by t.month