The solution for my problem:
select
OINV.DocTotal - OINV.PaidToDate as 'Offen', OINV.CardCode as 'Kundennummer', OINV.NumAtCard as 'DIAMOD Rechnungsnummer', OINV.DocNum as 'Dokumentennummer', max(ORCT.DocDate) as 'Zahlungsdatum', case when ORCT.DocCurr = (select MainCurncy from OADM) then RCT2.DcntSum else RCT2.DcntSumFC end as 'SkontoRechnungswährung',
RCT2.DcntSum as 'SkontoFirmenwährung'
from
JDT1 inner join
OJDT on JDT1.TransId = OJDT.TransId inner join
ORCT on OJDT.BaseRef = ORCT.DocNum inner join
RCT2 on ORCT.DocNum = RCT2.DocNum inner join
OINV on RCT2.BaseAbs = OINV.DocEntry
where
JDT1.TransType in ('24') and
OINV.U_I_Imported = 'Y' and
OINV.DocTotal - OINV.PaidToDate = 0
group by
OINV.NumAtCard, OINV.DocNum, OINV.CardCode, OINV.DocTotal - OINV.PaidToDate, ORCT.DocCurr, RCT2.DcntSum, RCT2.DcntSumFC
union all
select
OINV.DocTotal - OINV.PaidToDate as Offen, OINV.CardCode as 'Kundennummer', OINV.NumAtCard as 'DIAMOD Rechnungsnummer', OINV.DocNum as 'Dokumentennummer', max(OITR.ReconDate) as 'Zahlungsdatum',
0.0 as 'SkontoRechnungswährung',
0.0 as 'SkontoFirmenwährung'
from
OITR inner join
ITR1 on OITR.ReconNum = ITR1.ReconNum inner join
OINV on ITR1.SrcObjAbs = OINV.DocEntry
where
OINV.DocTotal - OINV.PaidToDate = 0 and ITR1.SrcObjTyp = 13 and OINV.U_I_Imported = 'Y'
group by
OINV.NumatCard, OINV.DocNum, OINV.CardCode, OINV.DocTotal - OINV.PaidToDate
union all
select
ORIN.DocTotal - ORIN.PaidToDate as Offen, ORIN.CardCode as 'Kundennummer', ORIN.NumAtCard as 'DIAMOD Rechnungsnummer', ORIN.DocNum as 'Dokumentennummer', max(OITR.ReconDate) as 'Zahlungsdatum',
0.0 as 'SkontoRechnungswährung',
0.0 as 'SkontoFirmenwährung'
from
OITR inner join
ITR1 on OITR.ReconNum = ITR1.ReconNum inner join
ORIN on ITR1.SrcObjAbs = ORIN.DocEntry
where
ORIN.DocTotal - ORIN.PaidToDate = 0 and ITR1.SrcObjTyp = 14 and ORIN.U_I_Imported = 'Y'
group by
ORIN.NumatCard, ORIN.DocNum, ORIN.CardCode, ORIN.DocTotal - ORIN.PaidToDate