I think you really mean
SELECT T1.Billno,T1.Billdate,T1.BillAmount,T1.TPTCharge,T1.LBCharge,T1.Nettotal,T1.Tax,T1.Discount,T1.CName,T1.ONo,T1.Vno,T2.Item,T2.qty,T2.Rate,T2.Rate_Typ,T2.Amount,T2.Tax
FROM Sales T1,Tempsales T2
WHERE T1.Billno=T2.Billno AND (T1.Billdate BETWEEN @Billdate1 AND @Billdate2)
ORDER BY T1.Billno