Oracle 18c

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create table some_table
(fromdate date, todate date,key_id number);
begin
 INSERT INTO some_table VALUES (to_date('1/01/2010','dd/mm/yyyy'),to_date('31/10/2010','dd/mm/yyyy'),100);
 INSERT INTO some_table VALUES (to_date('1/01/2011','dd/mm/yyyy'),to_date('31/12/2011','dd/mm/yyyy'),50);
 INSERT INTO some_table VALUES (to_date('1/01/2012','dd/mm/yyyy'),to_date('31/12/2012','dd/mm/yyyy'),50);
 INSERT INTO some_table VALUES (to_date('1/01/2013','dd/mm/yyyy'),to_date('31/12/2013','dd/mm/yyyy'),50);
 INSERT INTO some_table VALUES (to_date('1/01/2014','dd/mm/yyyy'),to_date('31/12/2014','dd/mm/yyyy'),50);
 INSERT INTO some_table VALUES (to_date('1/01/2015','dd/mm/yyyy'),to_date('12/10/2015','dd/mm/yyyy'),50);
 INSERT INTO some_table VALUES (to_date('13/10/2015','dd/mm/yyyy'),to_date('31/12/2015','dd/mm/yyyy'),50);
 INSERT INTO some_table VALUES (to_date('1/01/2016','dd/mm/yyyy'),to_date('21/02/2016','dd/mm/yyyy'),50);
 INSERT INTO some_table VALUES (to_date('22/02/2016','dd/mm/yyyy'),to_date('31/12/2016','dd/mm/yyyy'),67);
 INSERT INTO some_table VALUES (to_date('1/01/2017','dd/mm/yyyy'),to_date('2/10/2017','dd/mm/yyyy'),67);
 INSERT INTO some_table VALUES (to_date('3/10/2017','dd/mm/yyyy'),to_date('31/12/2017','dd/mm/yyyy'),75);
 INSERT INTO some_table VALUES (to_date('1/01/2018','dd/mm/yyyy'),to_date('31/03/2018','dd/mm/yyyy'),75);
 INSERT INTO some_table VALUES (to_date('1/04/2018','dd/mm/yyyy'),to_date('30/06/2018','dd/mm/yyyy'),75);
 INSERT INTO some_table VALUES (to_date('1/07/2018','dd/mm/yyyy'),to_date('31/10/2018','dd/mm/yyyy'),40);
 INSERT INTO some_table VALUES (to_date('1/11/2018','dd/mm/yyyy'),to_date('31/12/2018','dd/mm/yyyy'),75);
 INSERT INTO some_table VALUES (to_date('1/01/2019','dd/mm/yyyy'),to_date('31/03/2019','dd/mm/yyyy'),75);
 INSERT INTO some_table VALUES (to_date('1/04/2019','dd/mm/yyyy'),to_date('31/12/2019','dd/mm/yyyy'),75);
 INSERT INTO some_table VALUES (to_date('1/01/2020','dd/mm/yyyy'),to_date('1/03/2020','dd/mm/yyyy'),75);
end;
/
1 rows affected

SELECT t.key_id
      ,MIN(fromdate)
      ,MAX(todate)
FROM   (SELECT t.*
              ,row_number() over(ORDER BY fromdate) AS startseq
              ,row_number() over(PARTITION BY t.key_id ORDER BY fromdate) AS endseq
        FROM   some_table t) t
GROUP  BY t.key_id
         ,(startseq - endseq);


KEY_ID
MIN(FROMDATE)
MAX(TODATE)


50
01-JAN-11
21-FEB-16

100
01-JAN-10
31-OCT-10

67
22-FEB-16
02-OCT-17

40
01-JUL-18
31-OCT-18

75
03-OCT-17
30-JUN-18

75
01-NOV-18
01-MAR-20
KEY_ID	MIN(FROMDATE)	MAX(TODATE)
50	01-JAN-11	21-FEB-16
100	01-JAN-10	31-OCT-10
67	22-FEB-16	02-OCT-17
40	01-JUL-18	31-OCT-18
75	03-OCT-17	30-JUN-18
75	01-NOV-18	01-MAR-20