테이블 설계가 왜 저런지 -_-;;;

하기 쿼리 참고하세요..

---쿼리시작---

;With a(PK_ID,name,Subject,Content) As
(
      Select 1,'AAA','1번문제','1번문제입니다' Union All
      Select 2,'BBB','2번문제','2번문제입니다' Union All
      Select 3,'CCC','3번문제','3번문제입니다' Union All
      Select 4,'DDD','4번문제','4번문제입니다'
)
,b(a_PK_ID,name,Content,RegDate) As
(
      Select 1,'EEEE','1번정답입니다','2016-08-23' Union All
      Select 2,'FFFF','2번정답입니다','2016-08-23' Union All
      Select 3,'GGG' ,'3번정답입니다','2016-08-23' Union All
      Select 4,'HHH' ,'4번정답입니다','2016-08-23'
)
,c(a_PK_ID,name,content,RegDate) As
(
      Select 1,'VVV','1번정답이 아닌거 같습니다','2016-09-02' Union All
      Select 1,'ERr','1번정답이 아닌거 같습니다','2016-09-04' Union All
      Select 1,'AAA','1번정답이 아닌거 같습니다','2016-09-13' Union All
      Select 2,'BBB','2번정답이 아닌거 같습니다','2016-09-19' Union All
      Select 2,'FFF','2번정답이 아닌거 같습니다','2016-09-24' Union All
      Select 4,'JKU','4번정답이 아닌거 같습니다','2016-09-21' Union All
      Select 4,'DDD','4번정답이 아닌거 같습니다','2016-09-22'
)
      Select a.PK_ID  As NO
            ,a.name   As name
            ,a.Subject As subject
            ,IsNull(d.RegDate,'') As RegDate
        From a
               Left Outer Join
                               (
                                     Select d.a_PK_ID
                                           ,d.RegDate As RegDate
                                       From
                                           (
                                                Select b.a_PK_ID
                                                      ,b.RegDate
                                                      ,1 As seq
                                                  From b
                                                 Where Not Exists (
                                                                       Select 'x'
                                                                         From c
                                                                        Where b.a_PK_ID = c.a_PK_ID
                                                                  )   
                                          
                                             Union All      
                                          
                                                Select c.a_PK_ID
                                                      ,c.RegDate
                                                      ,Row_Number() Over(Partition By c.a_PK_ID Order By c.RegDate Desc) As seq
                                                  From c
                                           ) d
                                      Where d.seq = 1
                               )
                                 d
                                   On  a.PK_ID = d.a_PK_ID
---쿼리끝---     

두분다 대단하십니다  늘 고맙습니다