Oracleを使用して、3つのテーブルをPIVOTで1つに結合します

これでうまくいくはずです-

CREATE TABLE users
    (user_id varchar2(9), user_name varchar2(11))
;

INSERT ALL 
    INTO users (user_id, user_name)
         VALUES ('1', 'user_1')
    INTO users (user_id, user_name)
         VALUES ('2', 'user_2')
    INTO users (user_id, user_name)
         VALUES ('3', 'user_3')
    INTO users (user_id, user_name)
         VALUES ('4', 'user_4')
SELECT * FROM dual
;

CREATE TABLE exam
    (exam_id varchar2(9), exam_name varchar2(11))
;

INSERT ALL 
    INTO exam (exam_id, exam_name)
         VALUES ('1', 'exam_1')
    INTO exam (exam_id, exam_name)
         VALUES ('2', 'exam_2')
    INTO exam (exam_id, exam_name)
         VALUES ('3', 'exam_3')
SELECT * FROM dual
;

CREATE TABLE exam_user
    (exam_id varchar2(9), user_id varchar2(9), exam_date varchar2(11))
;

INSERT ALL 
    INTO exam_user (exam_id, user_id, exam_date)
         VALUES ('1', '1', '2017')
    INTO exam_user (exam_id, user_id, exam_date)
         VALUES ('1', '2', '2018')
    INTO exam_user (exam_id, user_id, exam_date)
         VALUES ('1', '3', '2017')
    INTO exam_user (exam_id, user_id, exam_date)
         VALUES ('2', '3', '2018')
SELECT * FROM dual
;

クエリ-

SELECT * FROM (
SELECT U.USER_ID, U.USER_NAME, E.EXAM_NAME,EU.EXAM_DATE
FROM USERS U, EXAM E, EXAM_USER EU
WHERE U.USER_ID = EU.USER_ID(+)
AND E.EXAM_ID(+) = EU.EXAM_ID
ORDER BY U.USER_ID
  )
  PIVOT (MAX(EXAM_DATE) FOR EXAM_NAME IN ('exam_1' as exam_1, 'exam_2' as exam_2,'exam_3' as exam_3))
  order by 1
;

出力-

USER_ID USER_NAME   EXAM_1  EXAM_2  EXAM_3
1   user_1  2017    (null)  (null)
2   user_2  2018    (null)  (null)
3   user_3  2017    2018    (null)
4   user_4  (null)  (null)  (null)