SQL 2 Left outer joins with Sum and Group By - sql

Question

Looking for some guidance on this. I am attempting to run a report in my complaint management system.. Complaints by Year, Location, Subcategory, Showing Totals for TotalCredits (child table) and TotalsCwts (childtable) as well as total ExternalRootCause (on master table).
This is my SQL, but the TotalCwts and TotalCredits are not being calculated correctly. It calculates 1 time for each child record rather than the total for each master record.
SELECT
dbo.Complaints.Location,
YEAR(dbo.Complaints.ComDate) AS Year,
dbo.Complaints.ComplaintSubcategory,
COUNT(Distinct(dbo.Complaints.ComId)) AS CustomerComplaints,
SUM(DISTINCT CASE WHEN (dbo.Complaints.RootCauseSource = 'External' ) THEN 1 ELSE 0 END) as ExternalRootCause,
SUM(dbo.ComplaintProducts.Cwts) AS TotalCwts,
Coalesce(SUM(dbo.CreditDeductions.CreditAmount),0) AS TotalCredits
FROM dbo.Complaints
JOIN dbo.CustomerComplaints
ON dbo.Complaints.ComId = dbo.CustomerComplaints.ComId
LEFT OUTER JOIN dbo.CreditDeductions
ON dbo.Complaints.ComId = dbo.CreditDeductions.ComId
LEFT OUTER JOIN dbo.ComplaintProducts
ON dbo.Complaints.ComId = dbo.ComplaintProducts.ComId
WHERE
dbo.Complaints.Location = Coalesce(#Location,Location)
GROUP BY
YEAR(dbo.Complaints.ComDate),
dbo.Complaints.Location,
dbo.Complaints.ComplaintSubcategory
ORDER BY
[YEAR] desc,
dbo.Complaints.Location,
dbo.Complaints.ComplaintSubcategory
Data Results
Location | Year | Subcategory | Complaints | External RC | Total Cwts | Total Credits
---------------------------------------------------------------------------------------
Boston | 2016 | Documentation | 1 | 0 | 8 | 8.00
Data Should Read
Location | Year | Subcategory | Complaints | External RC | Total Cwts | Total Credits
---------------------------------------------------------------------------------------
Boston | 2016 | Documentation | 1 | 0 | 4 | 2.00
Above data reflects 1 complaint having 4 Product Records with 1cwt each and 2 credit records with 1.00 each.
What do I need to change in my query or should I approach this query a different way?

Answer 1

The problem is that the 1 complaint has 2 Deductions and 4 products. When you join in this manner then it will return every combination of Deduction/Product for the complaint which gives 8 rows as you're seeing.
One solution, which should work here, is to not query the Dedustion and Product tables directly; query a query which returns one row per table per complaint. In other words, replace:
LEFT OUTER JOIN dbo.CreditDeductions ON dbo.Complaints.ComId = dbo.CreditDeductions.ComId
LEFT OUTER JOIN dbo.ComplaintProducts ON dbo.Complaints.ComId = dbo.ComplaintProducts.ComId
...with this - showing the Deductions table only, you can work out the Products:
LEFT OUTER JOIN (
select ComId, count(*) CountDeductions, sum(CreditAmount) CreditAmount
from dbo.CreditDeductions
group by ComId
) d on d.ComId = Complaints.ComId
You'll have to change the references to dbo.CreditDedustions to just d (or whatever you want to call it).
Once you've done them both then you'll one each per complaint, which will result with 1 row per complaint contaoining the counts and totals from the two sub-tables.