COUNT is incorrect when grouping?

Question

I am trying to display the employee number of each employee who manages other employees with the number of people he or she manages with the below table called emp.

empno  ename   job         mgr         hiredate    sal      comm       deptno
-----  ------  ----------  ----------  ----------  -------  -------    ------
7369   Smith   Clerk       7902        1980-12-17  800                 20
7499   Allen   Salesman    7698        1981-02-20  1600     300        30
7521   Ward    Salesman    7698        1981-02-22  1250     500        30
7566   Jones   Manager     7839        1981-04-02  2975                20
7654   Martin  Salesman    7698        1981-09-28  1250     1400       30
7698   Blake   Manager     7839        1981-05-01  2850                30
7782   Clark   Manager     7839        1981-06-09  2450                10
7788   Scott   Analyst     7566        1982-12-09  3000                20
7839   King    President               1981-11-17  5000                10
7844   Turner  Salesman    7698        1981-09-08  1500     0          30
7876   Adams   Clerk       7788        1983-01-12  1100                20
7900   James   Clerk       7698        1983-12-03  950                 30
7902   Ford    Analyst     7566        1983-12-13  3000                20
7934   Miller  Clerk       7782        1982-01-23  1300

Any idea of how I can go about doing this?

I have tried

select empno,count(mgr) from emp group by empno,mgr;

but this returns:

empno       count(mgr)
----------  ----------
7369        1
7499        1
7521        1
7566        1
7654        1
7698        1
7782        1
7788        1
7839        0
7844        1
7876        1
7900        1
7902        1
7934        1

Thanks so much for your help.

Answer 1

select count(*) from employee_table group by mgr

Answer 2

I would actualy group by mgr, then you'd have a group per manager and can just do a count to see how many persons that manager manages. Then, you could do a self join on the table to get that manager's info. Something like:

SELECT E1.Mgr, E2.ename, Count(*) as Number FROM Employees E1
INNER JOIN Employees E2 ON E1.mgr = E2.empno
GROUP BY E1.Mgr

Though I haven't tested this.