-1
This is very resource consuming, but your database doesn't seen big.
SELECT
t.ItemKey
,t.PostDate
,t.ReturnAmt
,t.ReturnsQty
,t.SalesAmt
,t.SalesQty
,t.TranDate
,(SELECT s.CustID FROM [dbo].[slSalesOrderTable] s WHERE t.CustKey = s.CustKey LIMIT 1) as CUSTID
FROM [dbo].[tsoSales...