Multiple joins in mysql tables with union - mysql

Question

In mysql, I am having an issue trying to get the right data. I think I have to use union to get all the results from both tables, but not sure how to do it.
Description of tables:
Order holds order numbers
Employee holds the employee
Zone holds the zones names
Actual time has the zone id, the order id and the amount of hours it should take to deliver
Deliver details contains the employee id, the zone the employee delivered and the amount of hours it took to deliver
Order
| id | number |
|----|--------|
| 1 | 0001 |
employees
| id | name |
|----|------|
| 1 | Jon |
zones
| id | name |
|----|-------|
| 1 | ZoneA |
| 2 | ZoneB |
actual_times
| id | zone_id | eta_hours | order_id |
|----|---------|-----------|----------|
| 1 | 1 | 5 | 1 |
| 2 | 2 | 4 | 1 |
deliver_details
| id | order_id | employee_id | zone_id | hours |
|----|----------|-------------|---------|-------|
| 1 | 1 | 1 | 1 | 3 |
| 2 | 1 | 1 | 1 | 1 |
What I am hoping to get is the zone name, the amount of hours it takes to deliver and the sum of hours the employee took deliver. If the employee did not deliver to that zone then show 0
Expected output
| zone_name | hours | eta_hours | employee_name |
|-----------|-------|-----------|---------------|
| ZoneA | 4 | 5 | Jon |
| ZoneB | 0 | 4 | Jon |
I tried making a union all on the actual time but I am not getting it right.
This is something I tried (note that this was just to get the right zones with deliver times and actual times).
SELECT deliver_details.zone_id, actual_times.zone_id, zones.zone_name FROM actual_times
RIGHT JOIN deliver_details ON actual_times.order_id = deliver_details.order_id
INNER JOIN zones ON zones.id = deliver_details.zone_id
WHERE deliver_details.order_id = 1
GROUP BY deliver_details.zone_id
UNION ALL
SELECT deliver_details.zone_id, actual_times.zone_id, zones.zone_name FROM actual_times
LEFT JOIN deliver_details ON actual_times.order_id = deliver_details.order_id
INNER JOIN zones ON zones.id = actual_times.zone_id
WHERE actual_times.order_id = 1
group by actual_times.zone_id
I am pretty much trying to get all of this in one query. Is there a way to do this?
Please note that this is a simplification to a more complex problem I am having. If you need more explanation or something does not make sense, please let me know.

Answer 1

No need to use UNION.
Start from table employees, then CROSS JOIN with zones and actual_times to get a simple cartesian products. Then search the deliver_details for deliveries performed by each employee on each zone ; use a LEFT JOIN for that. If an epmplyee did not deliver on a given zone, use COALESCE to return 0 instead of NULL.
Query :
select
z.name,
coalesce(sum(dd.hours), 0),
at.eta_hours,
e.name
from
employees e
cross join zones z
inner join actual_times at on at.zone_id = z.id
left join deliver_details dd on dd.employee_id = e.id and dd.id = at.zone_id
group by
z.name, at.eta_hours, e.name

Answer 2

I came up with a simillar solution to GMB, but using UNION to get rows with 0 hours...:
SELECT z.name, sum(dd.hours), at.eta_hours, e.name
FROM zones z JOIN deliver_details dd ON z.id = dd.zone_id
JOIN actual_times at ON z.id = at.zone_id
JOIN employees e ON dd.employee_id = e.id
GROUP BY z.name, at.eta_hours, e.name
UNION
SELECT z.name, 0, at.eta_hours, e.name
FROM zones z JOIN actual_times at ON z.id = at.zone_id,
employees e
WHERE e.id NOT IN (SELECT employee_id FROM deliver_details WHERE zone_id = z.id)

Answer 3

If you have only one employee for each zone the following query should work for you:
SELECT Z.name AS zone_name
,DT.hours_total
,ACT.eta_hours_total
,E.name AS employee_name
FROM zones Z
INNER JOIN (SELECT zone_id
, SUM(eta_hours) eta_hours_total
FROM actual_times
GROUP BY zone_id) ACT ON Z.zone_id = ACT.zone_id
INNER JOIN (SELECT zone_id
, employee_id
, SUM(hours) hours_total
FROM deliver_details
GROUP BY zone_id, employee_id) DT ON Z.zone_id = DT.zone_id
INNER JOIN employees E ON DT.employee_id = E.employee_id