select

chassis_number as FAGNR, 
make_code as FTYPE, 
posting_date as REDAT,
posting_date as OPDAT, 
due_date as FLDAT, 
account_number as O500_KTONR, 
document_number as O500_BELEGNR1, 
entry_number as Reserve_1, 
transact_sum as REBEB, 
transact_outstanding as O500_HW2BETR_OFFEN, 
transact_sum as O500_HW2BUCHGBETR, 
customer_number as KNDNR,  
concat(customer_number,' - ', replace(replace(customer_name, "  ", " "), "'", "´")) as KNAME, 
customer_phone as KTELF, 
customer_address as KSTRA, 
customer_zipcode as KDPLZ,  
customer_city as KDORT,
salesman_user as KDBNR, 
salesman_number as KDBERA, 
salesman_name as KDBNAME, 
verkaeufer as Stufe5, 
reminder_level as Reserve_2,
case when transact_sum > 0 then 'R' else 'G' end as Reserve_3,
mahnstufe as O500_MAHNSTUFE, 
mahnstufe2 as Next_MAHNSTUFE, 
branch_code as Stufe3, 
filiale_nummer as FFIRM, 
'Forderungen DMS' as Stufe1,
kostenstelle_text as Stufe2,
'n.v.' as Stufe4,

branch_code as Betrieb,
shipment_date,
customer_number_leasing,
customer_name_leasing,
text1,
text2
  
  
from fm_rem_import as t1

INNER JOIN ( SELECT document_number, chassis_number, due_date, entry_number, MAX(reminder_level) as reminder_level
             FROM fm_rem_import 
			 GROUP BY 1, 2, 3, 4 ) AS t2 
  USING(document_number, chassis_number, due_date, entry_number, reminder_level)