SELECT dbo.tblPOLineItem.PONumber, Count(dbo.tblPOLineItem.PONumber) AS Total,
tblPurchaseOrders.RequestDate, tblPurchaseOrders.CostCenter
FROM dbo.tblPOLineItem INNER Join dbo.tblPurchaseOrders
ON tblPOLineItem.PONumber = tblPurchaseOrders.PONumber
GROUP BY dbo.tblPOLineItem.PONumber, tblPurchaseOrders.CostCenter, tblPurchaseOrders.RequestDate
ORDER BY Total DESC