我的SELECT错在哪里？（ 在树型结构中寻找叶子节点！）

[Amy2008]

表EMPLOYEE：
employeeID managerID
1 null
2 1
3 1
4 2
5 2
6 3
7 3
8 6
9 8
10 8

想找出没有任何下属的所有员工的姓名（即叶子节点），使用以下代码：
SELECT EmployeeID
FROM Employee
WHERE EmployeeID NOT IN
(SELECT DISTINCT ManagerID
FROM Employee
)

结果集却是空的！
分别调试子查询和外面的查询却是正确的！！

请各位指教！

[Chiff]

SELECT EmployeeID
FROM Employee
WHERE EmployeeID NOT IN
(SELECT DISTINCT isnull(ManagerID,'')
FROM Employee
)

[Yang_]

SELECT EmployeeID
FROM Employee a
WHERE not exists (SELECT 1 FROM Employee
where ManagerID=a.EmployeeID
)

[playyuer]

SELECT *
FROM Employee
WHERE EmployeeID IN
(SELECT ManagerID
FROM Employee
group by ManagerID
having count(*) =0
)

[j9988]

SELECT EmployeeID
FROM Employee a left join
(select SELECT DISTINCT ManagerID
FROM Employee where ManagerID is not null) b on a.EmployeeID=b.ManagerID
WHERE b.ManagerID is null

[Chiff]

playyuer(小干部儿) 的不对
having count(*) = 0 是不可能有结果的

[j9988]

SELECT EmployeeID
FROM Employee a left join
(select SELECT DISTINCT ManagerID
FROM Employee where ManagerID) b on a.EmployeeID=b.ManagerID
WHERE b.ManagerID is null

[WorldMobile]

全是高手，我就不出手了

:-)

[playyuer]

SELECT *
FROM Employee
WHERE EmployeeID not IN
(SELECT ManagerID
FROM Employee
where ManagerID is not null
group by ManagerID
)

[Chiff]

为什么要用group by呢？distinct不更好吗？

[Amy2008]

谢谢各位，几种方法都试过了，果然好使！！
分数不多，请各位笑纳....