SQL Count by criteria.

This one had me scratching my head for a while. I had a tiered query grouped by a number of fields in the table structure. I wanted to get a count of all applicable items matching a set of given statuses.

For example: Toys
Type
Manufacturer # Sold # Returned

Cars
--Vrroom 14 0
--Bigga 16 2
Dolls
--Munchkin 22 4
--Slimer 7 1

etc.

Originally I had a query along the lines of:
SELECT i.InventoryType,
p.ProductName,
m.ManufacturerName,
CASE t.TransactionType
WHEN 1
THEN 'Sold'
WHEN 2
THEN 'Returned'
ELSE 'N/A'
END AS TransactionStatus,
COUNT(t.TransactionID) AS TransactionCount
FROM Inventory i
INNER JOIN Product p ON i.InventoryID = p.InventoryID
INNER JOIN Manufacturer m ON p.ManufacturerID = m.ManufacturerID
INNER JOIN Transaction t ON p.ProductID = t.ProductID
WHERE .... -- Conditions...

(Now this is only a rough approximation of the issue I was facing)
I then grouped within the report and used a conditional field on the transaction status to count applicable items. It sort of worked, but produced 2 lines for the items that had both sales and returns:

Cars
--Vrroom 14 0
--Bigga 16 0
-- 0 2
Dolls
--Munchkin 22 0
-- 0 4
--Slimer 7 0
-- 0 1

At first this looked like an issue within the SSRS report where it was grouping by Details. I removed that grouping which at first looked like it was working (1 row per product manufacturer) but that just "knocked off" one of the values. (I.e. for "Bigga" I'd end up with either 16/0 or 0/2, essentially depending on which status was found first.)

Round 2: I went back to the query determined to do the grouping properly in SQL.

...
m.ManufacturerName,
CASE t.TransactionType
WHEN 1
COUNT(t.TransactionID)
ELSE
0
END AS SoldCount,
CASE t.TransactionType
WHEN 2
COUNT(t.TransactionID)
ELSE
0
END AS ReturnedCount
...

This required t.TransactionType to be in the GroupBy clause which resulted in query results pretty much identical to what I was seeing in the report.

Round 3:
...
m.ManufacturerName,
SUM(CASE t.TransactionType
WHEN 1
THEN 1
ELSE 0
END) AS SoldCount,
SUM(CASE t.TransactionType
WHEN 2
THEN 1
ELSE 0
END) AS ReturnedCount
...

And Bingo!

Cars
--Vrroom 14 0
--Bigga 16 2

Dolls
--Munchkin 22 4
--Slimer 7 1

(Also, if a transaction had a quantity you wanted to count by then it'd be summing on t.Quantity rather than "1" (transaction count))