使用MSSQL计算唯一出现的id

Question

我正在尝试计算每年独特的老师身份。我相信结果不是唯一的。

我的查询

SELECT DISTINCT count (tblTeachers.TeacherID) AS uniqueTeacherCount, tblSchoolYears.SchoolYear

FROM tblTeachers INNER JOIN tblTeacher_Building 
.
.

GROUP BY tblSchoolYears.SchoolYear
ORDER BY tblSchoolYears.SchoolYear DESC;

结果（计算TeacherID的副本）

我也试过

SELECT COUNT(DISTINCT tblTeachers.TeacherID) AS uniqueTeacherCount, tblSchoolYears.SchoolYear

FROM tblTeachers INNER JOIN tblTeacher_Building 
.
.

GROUP BY tblSchoolYears.SchoolYear
ORDER BY tblSchoolYears.SchoolYear DESC;

我错过了什么？

谢谢

Answer 1

Select Count(TeacherID) AS uniqueTeacherCount,SchoolYear
from
(
SELECT DISTINCT tblTeachers.TeacherID, tblSchoolYears.SchoolYear
FROM tblTeachers INNER JOIN tblTeacher_Building 
.
.
) hlp
GROUP BY SchoolYear
ORDER BY SchoolYear DESC;

Answer 2

你很亲密。我想这就是你要找的东西：

SELECT COUNT(*)
FROM
(
SELECT DISTINCT count (tblTeachers.TeacherID) AS uniqueTeacherCount, tblSchoolYears.SchoolYear ...
)