Apache Kylin 在 left outer join 后为何不支持+-*/运算啊？

• kylin sql

select
  a."member_num", b."member_num_tb", a."member_num" / b."member_num_tb"
from
(
    select
      count(distinct mobile) as "member_num"
      ,'week' as "dtype"
    from member
    where dweek <= '18.06.04~18.06.10'
) as a
left outer join
(
    select
      count(distinct mobile) as "member_num_tb"
      ,'week' as "dtype"
    from member
    where dweek_tb <= '18.06.04~18.06.10'
) as b on a."dtype" = b."dtype"

• 报错信息

That the right side of the BinaryTupleExpression owns columns is not supported for / while executing SQL: 
"select a."member_num", b."member_num_tb", a."member_num" / b."member_num_tb" from ( select count(distinct mobile) as "member_num" ,'week' as "dtype" from member where dweek <= '18.06.04~18.06.10' ) as a left outer join ( select count(distinct mobile) as "member_num_tb" ,'week' as "dtype" from member where dweek_tb <= '18.06.04~18.06.10' ) as b on a."dtype" = b."dtype" "

请问这是是什么原因啊？