SQL Server 2019

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create table the_table (nummer int, jahr int, mm int, sprache varchar(100), tools varchar(100));
insert into the_table (nummer, jahr, mm, sprache, tools)
values
  (1, 1981, 9, 'Assembler', 'EDOR'),
  (1, 1981, 9, 'Cobol', 'EDOR'),
  (1, 1981, 9, 'Assembler', 'EDT'),
  (1, 1981, 9, 'Cobol', 'EDT'),
  (1, 1981, 9, 'Assembler', 'etc.'),
  (1, 1981, 9, 'Cobol', 'etc.'),
  (2, 1981, 3, 'Basic', 'EDOR'),
  (2, 1981, 3, 'Pascal', 'EDOR'),
  (2, 1981, 3, 'Basic', 'FMS')
;
9 rows affected

select distinct jahr, mm, 
       (select string_agg(sprache, ',') 
        from (
          select distinct sprache 
          from the_table t2
          where t2.jahr = t1.jahr
            and t2.mm = t1.mm) s1) as sprachen,
       (select string_agg(tools, ',') 
        from (
          select distinct tools 
          from the_table t2
          where t2.jahr = t1.jahr
            and t2.mm = t1.mm) s2) as tools
from the_table t1



jahr
mm
sprachen
tools


1981
3
Basic,Pascal
EDOR,FMS

1981
9
Assembler,Cobol
EDOR,EDT,etc.