SQL CASE mixes up my grouping - sql-server

Question

The problem situates itself at the 4th line of the SELECT statement: CASE WHEN ct.TransactionReason=622 THEN ABS(ct.netquantity) ELSE c.RealNetWeight END AS NetWeight
When I add this line to the statement, my grouping will change. Instead of returning one line it now gives me back the amount of lines of different c.realnetweight.
Problem is that I only want to return one line. Sort of like a coalesce that when there is a ct.transactionreason = 622, it should give me ABS(ct.netquantity), otherwise the c.realnetweight. Code can be found beneath, suggestions would be very helpful. Thanks.
SELECT CASE WHEN P.Wrapped = 1 THEN T.[Level]+1 ELSE T.[Level] END AS [Level]
, #CoilId AS CoilId
, c.SupplierCoilID
, CASE WHEN ct.TransactionReason=622 THEN ABS(ct.netquantity) ELSE c.RealNetWeight END AS NetWeight
, C.RealGrossWeight
, p1.Description
, p1.product
, s.StackID
, s.ProductID
, s.Weight
, P.Product
, P.Description AS 'ProductDescription'
, COUNT(t.BlankId) AS 'NumberOfBlanks'
, c1.Description as 'Status'
, pv.ProductionWeight
, pv.BlankWeight
, t.BlankStatus
FROM #Trace T
INNER JOIN SKUTraceability SKUT ON SKUT.SKUID = T.SKUID
INNER JOIN Stack s ON SKUT.StackID = s.StackID
INNER JOIN Product p ON s.ProductID = p.ProductID
INNER JOIN Coil c ON c.CoilID=#CoilId
INNER JOIN CoilTransaction ct on ct.CoilID=#CoilId
INNER JOIN Product p1 ON c.ProductID=p1.ProductID
INNER JOIN Code c1 ON t.BlankStatus=c1.codenumber AND c1.codetypeid=17
INNER JOIN #ProductVersion pv ON pv.ProductID=p.ProductId AND s.ProductVersion = pv.ProductVersion
WHERE t.BlankId IS NOT NULL
GROUP BY T.[Level]
, c.SupplierCoilID
, CASE WHEN ct.TransactionReason=622 THEN ABS(ct.netquantity) ELSE c.RealNetWeight END
, c.RealGrossWeight
, p1.Description
, p1.product
, s.StackID
, s.ProductID
, s.Weight
, p.Product
, p.Description
, c1.Description
, pv.ProductionWeight
, pv.BlankWeight
, p.Wrapped
, t.BlankStatus

Answer 1

Hard to answer without understanding your table structures however, it appears that CoilTransaction is some sort of transaction table, i.e. a single product can have many transactions.
In your SELECT query, the line causing you issues, is the only line that references your CoilTransaction table therefore I believe, the reason you're returning multiple rows is because you're grouping on a value that is not unique. Also, are transactions individual items because you seem to have a quantity column on the table.
In short, you can't get the grouping you want by including those columns from your transaction table. You would need to elaborate more on what you're trying to accomplish for us to give a more suitable solution. What does that line mean?

Answer 2

For at least one CoilID in table Coil, you will have more than one value in the field netquantity in the table CoilTransaction. This is what is causing the increase in the number of records returned when you include this field in your CASE statement.
I would recommend finding the netquantity value that you want from CoilTransaction in a CTE, and then bringing this in to your CASE statement. For example:
;WITH transaction_summary AS (
SELECT
ct.CoilID,
ct.TransactionReason,
MAX(ct.netquantity) -- choose your aggregate function here
FROM
CoilTransaction ct
GROUP BY
ct.CoilID,
ct.TransactionReason
)
...