Oracle 18c

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ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
CREATE TABLE runtime (
  room_light VARCHAR2(20),
  "START"    VARCHAR2(20),
  ende       VARCHAR2(20),
  running    VARCHAR2(20)
);
INSERT INTO runtime (room_light, "START", ende, running)
SELECT '01', 'abc', 'def', 'Y' FROM DUAL UNION ALL
SELECT '01', 'ghi', 'jkl', 'Y' FROM DUAL UNION ALL
SELECT '01', 'mno', 'pqr', 'N' FROM DUAL UNION ALL
SELECT '02', 'stu', 'vwx', 'Y' FROM DUAL;
4 rows affected

SELECT JSON_OBJECT(
         KEY 'ROOM_LIGHT ' || ROOM_LIGHT VALUE JSON_ARRAYAGG(
           JSON_OBJECT(
             KEY 'START' VALUE "START",
             KEY 'ENDE'  VALUE ENDE,
             KEY 'RUN'   VALUE RUNNING
           )
         )
       ) As json
FROM   runtime
GROUP BY ROOM_LIGHT;


JSON


{"ROOM_LIGHT 01":[{"START":"abc","ENDE":"def","RUN":"Y"},{"START":"mno","ENDE":"pqr","RUN":"N"},{"START":"ghi","ENDE":"jkl","RUN":"Y"}]}

{"ROOM_LIGHT 02":[{"START":"stu","ENDE":"vwx","RUN":"Y"}]}