SQL， CTE, FLG CASE问题

求问大家一个SQL问题！我想求GROUP A-B的部分，并标记FLG为‘0’，Group B 为‘1’。已知GROUP A是520， GROUP B是5。FLG为‘0’则是515，但我还是得出520.大家能看下我的code吗？看是可能哪里出问题了,谢谢！

With PreMatricCTE as
(
SELECT DISTINCT
ID
,CASE
WHEN
(Group B的where) then 1 else end as CompletedFLG

FROM GROUP A
INNER JOIN GROUP B on A.ID = B.ID

GROUP BY ID
)

SELECT DISTINCT
ID
, MAX (CompletedFLG) as CompletedFLG

FROM PreMatricCTE

WHERE CompletedFLG = '0'

GROUOP BY ID