SQL Sum

Hi Experts,

I am looking to sum a total on an order however...  ive no idea how to pull it all together...

I have tried a nested query but it fails on me, not really don't nested queries before so struggling with it... however..

to get the list of results of an order back the SQL works, however... when adding the sum function it fails.

the SQL is

select 
o.OrderNumber, o.WorkOrderNumber, 
s.SupplierName, 
o.SupplierOrderNumber, o.OrderDate, o.DueDeliveryDate,
oi.item, oi.qty,oi.PriceatOrder, oi.itemtotalcost, 
oi.received
from SupplierOrders.Orders o
left join SupplierOrders.Suppliers s on s.SupplierID = o.SupplierID 
left join SupplierOrders.Order_Item oi on oi.OrderNumber = o.OrderNumber--
where 

o.OrderNumber = 27

select sum(oi.itemtotalcost) as OrderTotal 
from SupplierOrders.Orders o
left join SupplierOrders.Suppliers s on s.SupplierID = o.SupplierID 
left join SupplierOrders.Order_Item oi on oi.OrderNumber = o.OrderNumber--
where 
o.OrderNumber = 27

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