select
detail.Id,
detail.LineNumber,
detail.TotalUnits,
sum(invoiceSz.Units) SzUnits
from dbo.InvoiceDetailSizes invoiceSz
inner join dbo.InvoiceDetails detail on invoiceSz.InvoiceDetailId = detail.Id
where detail.InvoiceHeaderId = 278663
group by detail.Id, detail.LineNumber, detail.TotalUnits
order by detail.LineNumber