select a.AbonentID, e.PeriodBegin, e.PeriodEnd, (select distinct (e.CE_Discharge)) V, Round((g.TariffG*((e.CE_Discharge)-(18.3*p.PrivilegePercent*0.01))),2) as NACHISL,
SUM(pa.PaySumm) as OPL, Round((g.TariffG*((e.CE_Discharge)-(18.3*p.PrivilegePercent*0.01))),2) - SUM(pa.PaySumm) as DOLG
 from Abonents a
left join Evidences e on a.AbonentID = e.AbonentID
left join Privileges p on a.PrivilegeID = p.PrivilegeID
left join GasTariffs g on a.GasID = g.GasID
left join Pays pa on a.AbonentID = pa.AbonentID
 where e.IsGas = 'True' and e.PeriodBegin = pa.PeriodBegin and e.PeriodEnd = pa.PeriodEnd
GROUP BY a.AbonentID, e.IsGas, e.PeriodBegin, e.PeriodEnd, e.CE_Discharge, g.TariffG, p.PrivilegePercent