MySQL Multiple Group-By Count - mysql

Question

I'm trying to count some results from a query. I've been through the various examples on here but none of them are adaptable enough to do what I'm trying to do.
If someone could take a look, point out where I'm going wrong, and kindly put me out of my misery, that would be wonderful. Thank-you.
Four Tables: Areas, Departments, Systems and Checks
Each Area has many Departments. Each Department has many Systems; and each System has many Checks. I'm trying to find out how many different Systems (by System_ID) have been checked in the previous week.
Current Query
Select
a.Area_Name,
d.Department_Name,
s.System_ID,
s.System_Name,
c.Check_Date
from departments d
left join areas a
on a.Area_ID = d.Department_Area
left join systems s
on s.System_Department = d.Department_ID
left join checks c
on c.Check_System_ID = s.System_ID
where Week(c.Check_Date) = Week(Now())
and Year(c.Check_Date) = Year(Now())
Returns the Following :
Area_Name | Department_Name | System_ID | System_Name | Check_Date
Area 1 Department 1 1 System 1 2017-02-27
Area 1 Department 1 1 System 1 2017-02-27
Area 1 Department 1 2 System 2 2017-02-27
Area 1 Department 2 3 System 3 2017-02-27
What I'm trying to get to will group the areas, departments, systems etc. To show a count of how many different systems have been checked in the week.
(I'm aware I haven't included any count or group-by in the query... I've left them out purposely to provide context. I have tried every possible way I can think but my knowledge is obviously lacking somewhere)
Desired Result
Area_Name | Department_Name | Count_Checks
Area 1 Department 1 2
Area 1 Department 2 1
As you can see, the desired result has grouped the two System 1 and treated them as 1 (as it's a single unique system), to show that over the last week, 2 different systems have been checked from department 1 and only 1 from department 2.
If anyone can shed some light... please do!
Thanks in advance for any help!

Answer 1

Use GROUP BY and aggregate using a combination of area/department as group:
SELECT a.Area_Name,
d.Department_Name,
COUNT(DISTINCT s.System_ID) AS Count_Checks
FROM departments d
LEFT JOIN areas a
ON a.Area_ID = d.Department_Area
LEFT JOIN systems s
ON s.System_Department = d.Department_ID
LEFT JOIN checks c
ON c.Check_System_ID = s.System_ID AND
WEEK(c.Check_Date) = WEEK(NOW()) AND
YEAR(c.Check_Date) = YEAR(NOW())
GROUP BY a.Area_Name,
d.Department_Name
One part of the query which might not be obvious is the code used to determine Count_Checks:
COUNT(DISTINCT s.System_ID)
This will count, for each area/department group, the number of distinct system ID values. In the case of Area 1/Department 1, this would yield a distinct system count of 2, while for Area 1/Department 2, this would give a count of just 1.