Try this:
SELECT t1.*, SUM(t1.Amount) AS Total
FROM (
SELECT AllocateAsset.Item, AllocateAsset.ItemModel, Count(AllocateAsset.ItemModel) AS CountOfItem,
(CountOfItem*(SELECT Rate FROM rateList WHERE rateList.MakeModel=AllocateAsset.ItemModel ))/4 AS Amount
FROM aboutPM INNER JOIN
(AllocateAsset INNER JOIN
PMReport ON AllocateAsset.ID=PMReport.AssetID) ON aboutPM.ID=PMReport.AboutPMID
WHERE (((aboutPM.Year)="2015") AND ((aboutPM.Period)="Jan-Feb-Mar"))
GROUP BY AllocateAsset.Item, AllocateAsset.ItemModel
ORDER BY AllocateAsset.Item;
) AS t1
GROUP BY t1.Item, t1.ItemModel, t1.CountOfItem
Does
Year
field is varchar data type? It should be
numeric(integer)
data type!