-- First Create the #Temp Table ... 

SELECT
DISTINCT
j.ID AS 'ID',
j.inquiryRef AS 'EnquiryRef' ,
CAST( dbo.BigIntToDate(mod.date) AS DateTime) AS 'EnquiryDate',
j.jobRef AS 'JobReference' ,
CAST( dbo.GetJobDate(j.Id) AS DateTime) AS 'JobDate',
si.tranref AS 'InvoiceNumber', j.inquiryLogged,0 As CostOfSales -- here we added the cost of Sale in #Temp Table.
INTO #temp1
FROM
Job AS j
LEFT OUTER JOIN Modification mod ON mod.id = j.inquiryLogged
LEFT OUTER JOIN SalesInvoice si ON si.job = j.id

--Now the update Query for the updating the CostOfSales. 

Update t Set CostofSales = f.CostOfSales  From #Temp t Inner Join 
(
SELECT j.inquiryLogged,
SUM(CASE
WHEN ISNULL(jce.actualCost,0)<>0 THEN jce.actualCost
WHEN ISNULL(jce.actualCost,0)=0 and ISNULL(jce.manualOverRide,0)<>0 THEN jce.manualOverRide
ELSE ISNULL(jce.originalEstimate,0)
END) AS 'CostofSales'
FROM
Job AS j
LEFT OUTER JOIN JobCostElements jce ON j.Id = jce.job
LEFT OUTER JOIN Modification mod ON mod.id = j.inquiryLogged
WHERE mod.[date] BETWEEN @FromDate AND @ToDate
Group by j.inquiryLogged
) As  F
On f.inquiryLogged = t.inquiryLogged