oracle 10g通过引发列数相同的异常来选择组

它正在抛出异常

 select 
        case when exists (select "CreatedOn" dategn from "RentedVehicle" where "fkTempVehicleId"=3) 
        then 
        case when exists (select "CreatedOn" dategn from "Transfer" where "fkTempVehicleId"=3) 
        then 
           (select 
           case when rent.dategn>tran.dategn then rent.dategn else tran.dategn end dategn,
           case when rent.dategn>tran.dategn then rent.fuel else tran.fuel end fuel
           from 
              (
               select max("CreatedOn") dategn,"CheckInFuel" fuel 
               from "RentedVehicle" where "fkTempVehicleId"=3 
               group by "RentedVehicle"."CheckInFuel"
              ) rent ,
        (select max("CreatedOn") dategn,"fkFuelLevelId" fuel 
        from "Transfer" where "fkTempVehicleId"=3 group by "Transfer"."fkFuelLevelId") tran) 
        else 
        (select
         max("CreatedOn") dategn,"CheckInFuel" fuel 
        from "RentedVehicle" where "fkTempVehicleId"=3 group by "RentedVehicle"."CheckInFuel") end 
        else 
        case when exists (select "CreatedOn" dategn from "Transfer" where "fkTempVehicleId"=3) 
        then 
        (select max("CreatedOn") dategn,"fkFuelLevelId" fuel 
        from "Transfer" where "fkTempVehicleId"=3 group by "Transfer"."fkFuelLevelId") 
        else 
        (select "CreatedOn" dategn,"InitialFuel" fuel from "TempVehicle" where "pkTempVehicleId"=3) 
        end end  from dual;

我肯定我错过了一些东西，但我几乎尝试了所有东西。

---

请帮助并详细说明我遗漏了什么

案例语句的内联选择部分返回两个值dategn和fuel，其中只允许一个值：

ORA-00913: too many values
00913. 00000 -  "too many values"
*Cause:    
*Action:
Error at Line: 6 Column: 2

---

case在每行调用时，每行只能返回一个值。

我删除了这一行，case when rent.dategn>tran.dategn然后rent.fuel else tran.fuel end fuel。相同的Error@KhurramZulfiqarAli-您的最终选择，选择CreatedOn dategn，初始化来自TempVehicle的燃油，其中pkTempVehicleId=3，也有两个值。还有之前的那个。检查错误中的行号很有用。也许您需要一种新的方法来解决您的问题。据我所知，您正在尝试从三个表中选择TempVehicle、Transfer、RentedVehicle，但从未加入它们。有两个表具有外键fkTempVehicleId，现在我必须通过提供外键来选择任何表中存在的最新记录。如果两个表都没有该id的记录，那么我必须从它自己的表中选择这些记录。@KhurramZulfiqarAli:然后它发送，好像您最好合并单独的结果，以便获得一致的列计数，在内联视图中包装这些记录，并根据您的条件选择适当的数据集。

...
then 
(select 
case when rent.dategn>tran.dategn then rent.dategn else tran.dategn end dategn,
case when rent.dategn>tran.dategn then rent.fuel else tran.fuel end fuel
from ...