Oracle：未按表達式分組錯誤

Question

select case when x.a in (select y.c from join2) then x.a end, x.b, x.c, y.a, z.c 
from join1 x, join2 y, join3 z where x.a = z.a 
group by x.a, x.b, x.c, y.a, z.c order by x.c; 

運行此查詢時，我得到的是按表達式分組的error ORA-00979。我已經嘗試過從組中刪除x.a，但仍然無法運行。任何機構都可以幫助我做到這一點。

Answer 1

你需要在你的GROUP BY條款，而不是x.a這個表達式：

case when x.a in (select y.c from join2) then x.a end 

所以把他們放在一起：

SELECT CASE WHEN x.a IN (SELECT y.c FROM join2) THEN x.a END 
    , x.b, x.c, y.a, z.c 
    FROM join1 x, join2 y, join3 z 
WHERE x.a = z.a 
GROUP BY CASE WHEN x.a IN (SELECT y.c FROM join2) THEN x.a END 
    , x.b, x.c, y.a, z.c 
ORDER BY x.c; 

我必須指出，然而，你」重新進行x和y之間的笛卡爾連接，並且不完全清楚爲什麼您使用GROUP BY，因爲沒有聚合。