SQL Reloaded: List Based Aggregations (On Hand example)

    I found some time ago a query like the one below (I wrote this kind of queries myself too):
SELECT PP.Name
, PP.ProductNumber
, PP.MakeFlag
, PP.FinishedGoodsFlag
, IsNull(PI1.Quantity, 0) OnHandPaintStorage
, IsNull(PI2.Quantity, 0) OnHandFrameForming
, IsNull(PI3.Quantity, 0) OnHandFrameWelding
, IsNull(PI1.Quantity, 0)+IsNull(PI2.Quantity, 0)+IsNull(PI3.Quantity, 0) OnHand
, PP.ListPrice
, PP.StandardCost
, (IsNull(PI1.Quantity, 0)+IsNull(PI2.Quantity, 0)+IsNull(PI3.Quantity, 0))*PP.StandardCost Value
FROM Production.Product PP
LEFT JOIN
(-- On Hand Paint Storage
SELECT SUM (Quantity) Quantity
, PPI.ProductID
FROM Production.ProductInventory PPI
JOIN Production.Location PL
ON PPI.LocationID = PL.LocationID
WHERE PL.Name = 'Paint Storage' GROUP BY PPI.ProductID
) PI1
ON PP.ProductID = PI1.ProductID
LEFT JOIN
(--On Hand Frame Forming
SELECT SUM (Quantity) Quantity
, PPI.ProductID
FROM Production.ProductInventory PPI
JOIN Production.Location PL
ON PPI.LocationID = PL.LocationID
WHERE PL.Name = 'Frame Forming'
GROUP BY PPI.ProductID
) PI2
ON PP.ProductID = PI2.ProductID
LEFT JOIN
(--On Hand Frame Welding
SELECT SUM (Quantity) Quantity
, PPI.ProductID
FROM Production.ProductInventory PPI
JOIN Production.Location PL
ON PPI.LocationID = PL.LocationID
WHERE PL.Name = 'Frame Welding'
GROUP BY PPI.ProductID
) PI3
ON PP.ProductID = PI3.ProductID
WHERE IsNull(PI1.Quantity, 0)+IsNull(PI2.Quantity, 0)+IsNull(PI3.Quantity, 0) <> 0
ORDER BY PP.Name

    I exemplified the above query by using tables from AdventureWorks database, and it's based on Product, ProductInventoy and Location table.
The query returns the OnHand from special Locations (here I exemplified with only 3 locations, but could be more), the query is not difficult even if it involves 3 tables, however many people write this kind of lengthy queries. A much simpler solution is to use directly aggregations as in the below query. Such method is flexible enough to allow to add another Locations to the query in no time, and performs better!
SELECT PP.Name
, PP.ProductNumber
, PP.MakeFlag
, PP.FinishedGoodsFlag
, SUM(CASE WHEN PL.Name = 'Paint Storage' THEN PPI.Quantity ELSE 0 END) OnHandPaintStorage
, SUM(CASE WHEN PL.Name = 'Frame Forming' THEN PPI.Quantity ELSE 0 END) OnHandFrameForming
, SUM(CASE WHEN PL.Name = 'Frame Welding' THEN PPI.Quantity ELSE 0 END) OnHandFrameWelding
, SUM(CASE WHEN PL.Name = 'Debur and Polish' THEN PPI.Quantity ELSE 0 END) OnHandDeburPolish
, SUM(CASE WHEN PL.Name = 'Specialized Paint' THEN PPI.Quantity ELSE 0 END) OnHandSpecializedPaint
, SUM(CASE WHEN PL.Name = 'Subassembly' THEN PPI.Quantity ELSE 0 END) OnHandSubassembly
, SUM(CASE WHEN PL.Name = 'Final Assembly' THEN PPI.Quantity ELSE 0 END) OnHandFinalAssembly
, SUM(PPI.Quantity) OnHand
, PP.ListPrice
, PP.StandardCost
, SUM(PPI.Quantity)*PP.StandardCost Value
FROM Production.ProductInventory PPI
JOIN Production.Product PP
ON PPI.ProductID = PP.ProductID
JOIN Production.Location PL
ON PPI.LocationID = PL.LocationID
WHERE PL.Name IN ('Paint Storage', 'Frame Forming', 'Frame Welding', 'Debur and Polish', 'Specialized Paint', 'Subassembly', 'Final Assembly')
GROUP BY PP.Name
, PP.ProductNumber
, PP.MakeFlag
, PP.FinishedGoodsFlag
, PP.ListPrice
, PP.StandardCost
HAVING SUM(PPI.Quantity)<>0
ORDER BY PP.Name

Note:
1. Probably you'll wonder why I put the constraint SUM(PPI.Quantity)<>0?! The explanation is simple, I met cases in which ERP systems were allowing negative values for On Hand, pretty cool, isn't it?
2. AdventureWorks database can be downloaded from Microsoft site.
3. I met many other cases in which this type of quries are very handy, in here I tried to exemplify the method in the easiest possible way, with minimum of effort :D.