统计两个表的问题

Question

加個別名Select 部门数=COUNT( * ) From
( Select d_no From FirstDepartment
Union
Select d_no From SecondDepartment)a

Answer 1

Select T.COUNT( * ) From
(
    Select d_no From FirstDepartment
    Union
    Select d_no From SecondDepartment
) as T

Answer 2

Select T.COUNT( * ) From(Select d_no From FirstDepartment Union
                         Select d_no From SecondDepartment) as table

Answer 3

Select T.COUNT( * ) From
(
    Select d_no From FirstDepartment
    Union
    Select d_no From SecondDepartment
) as T同意

Answer 4

Select T.COUNT( * ) From
(
    Select d_no From FirstDepartment
    Union
    Select d_no From SecondDepartment
) as T
我的SQL