선택 항목의 중첩 된 케이스

Question

내 실수는 어디에 있나요?

select dr.ders_code, dr.year, 
case when dr.muf_sq is not null then 
case when (select muf_sq_id from mufredat_sq m join ders_stud_ref dr on dr.muf_sq = m.muf_sq_id) = dr.muf_sq then dr.muf_sq end 
end 
from ders_stud_ref dr 

Answer 1

첫 번째 실수는

select muf_sq_id 
       from mufredat_sq m 
       join ders_stud_ref dr on dr.muf_sq = m.muf_sq_id 

보다 한 행 한 후 반환 할 수 있습니다

난 당신이

문제/오류가

select dr.ders_code, dr.year, 
case when dr.muf_sq is not null then 
case when exists (select muf_sq_id 
      from mufredat_sq m 
      where dr.muf_sq = m.muf_sq_id) then dr.muf_sq end 
end 
from ders_stud_ref dr