How to get data status wise after grouping? - mysql

Question

I want to get count of different statuses for bookings for each event and some other data. Each row should represent an event.
So I have an events table and a bookings table.
Events table has id, name, max_allowed
Bookings table has id,event_id,status
Status can be booked, canceled, waitlisted.
I want to get data for all events with the count for each status.
So I need these columns -
event_id
booked_count
canceled_count
waitlisted_count
remaining_slots - (max_allowed - booked_count)
occupancy_rate - booked_count/max_allowed
Sample data:
Events
| id | name | max_allowed |
|---- |--------- |------------- |
| 1 | Yoga | 5 |
| 2 | Boxing | 2 |
| 3 | Pilates | 5 |
Bookings
| id | event_id | status |
|---- |---------- |------------ |
| 1 | 1 | booked |
| 2 | 1 | booked |
| 3 | 2 | booked |
| 4 | 2 | canceled |
| 5 | 2 | booked |
| 6 | 2 | waitlisted |
| 7 | 3 | booked |
| 8 | 3 | booked |
| 9 | 3 | booked |
Output:
| event_id | booked_count | canceled_count | waitlisted_count | remaining_slots | occupancy_rate |
|---------- |-------------- |---------------- |------------------ |----------------- |---------------- |
| 1 | 2 | 0 | 0 | 3 | 0.4 |
| 2 | 2 | 1 | 1 | 0 | 1 |
| 3 | 3 | 0 | 0 | 2 | 0.6 |

Answer 1

Use conditional aggregation:
select t.*,
greatest(0, t.max_allowed - t.booked_count + t.canceled_count - t.waitlisted_count) remaining_slots,
least(t.max_allowed, t.booked_count - t.canceled_count + t.waitlisted_count) / t.max_allowed occupancy_rate
from (
select e.id, e.name, e.max_allowed,
sum(status = 'booked') booked_count,
sum(status = 'canceled') canceled_count,
sum(status = 'waitlisted') waitlisted_count
from Events e left join Bookings b
on b.event_id = e.id
group by e.id, e.name, e.max_allowed
) t

Answer 2

Try below query.
with src_data as
(select
event_id,
sum(case when status='booked' then 1 else 0 end ) as booked_count,
sum(case when status='canceled' then 1 else 0 end ) as canceled_count,
sum(case when status='waitlisted' then 1 else 0 end ) as waitlisted_count
from bookings group by event_id
)
select
s.event_id,
s.booked_count,
s.canceled_count,
s.waitlisted_count,
e.max_allowed-s.booked_count,
s.booked_count/e.max_allowed
from events e inner join src_data s
on e.id=s.event_id;