SELECT to_char(DATE_,'dd-mm') as daymonth FROM work_days
JOIN
(SELECT to_char(CREATED_ON,'dd-mm') as creation2016, COUNT(CREATED_ON)
FROM cuba.DS_HD_ISSUE_LIST_2017
WHERE CREATED_ON BETWEEN /*'01.10.2015'*/sysdate - INTERVAL  '15' month AND (sysdate - INTERVAL '1' year)
GROUP BY to_char(CREATED_ON,'dd-mm'))
creation2016 on creation2016.creation2016 = work_days.daymonth
JOIN ( SELECT to_char(CREATED_ON,'dd-mm') as creation2017
FROM cuba.DS_HD_ISSUE_LIST_2017
WHERE CREATED_ON BETWEEN /*'01.10.2016'*/ sysdate - INTERVAL  '3' month AND sysdate
GROUP BY  to_char(CREATED_ON,'dd-mm'))
creation2017 on creation2017.creation2017 = work_days.daymonth;