SELECT to_char(DATE_, 'dd-mm') as daymonth
  FROM nnu.work_days wd
  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 = to_char(wd.DATE_,'dd-mm')
  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  = to_char(wd.DATE_,'dd-mm')
  where wd.YEAR_ = 2016
  ;