Hi Sean
The solution I was looking for is something like this :
SELECT
p.ProductID,
Dept1ProdCount = COUNT(CASE WHEN t.ProductSoldInDept1 = p.ProductID THEN 1 END),
Dept2ProdCount = COUNT(CASE WHEN t.ProductSoldInDept2 = p.ProductID THEN 1 END),
Dept3ProdCount = COUNT(CASE WHEN t.ProductSoldInDept3 = p.ProductID THEN 1 END)
FROM dbo.Product AS p
LEFT OUTER JOIN dbo.[Transaction] AS t
ON p.ProductID IN
(t.ProductSoldInDept1, t.ProductSoldinDept2, t.ProductSoldinDept3)
GROUP BY p.ProductID;
Thank you !