Hi Geoff,
Try:
SELECT T0.[ItemCode], T0.[ItemName], T0.[OnHand]'Physical_Stock', T0.[IsCommited]'On_Sales_Order', T0.[OnOrder]'On_Purchase_Order',
CASE WHEN t0.onorder=0 THEN null ELSE min(T2.[ShipDate])
end as 'Expected_Delivery',SUM(T1.[Quantity])'Invoiced_Qty_12_months'
FROM OITM T0
LEFT JOIN INV1 T1 ON T0.ItemCode = T1.ItemCode
LEFT JOIN POR1 T2 ON T0.ItemCode = T2.ItemCode AND DateDiff(dd,T2.ShipDate,GetDate())<0
WHERE T0.[ItemCode] like 'COV%'
GROUP BY T0.[ItemCode], T0.[ItemName], T0.[OnHand], T0.[IsCommited], T0.[OnOrder]
Thanks,
Gordon