Finding the first X with exactly one Y

Question

Suppose you have a table DEPT_EMP with columns DEPT and EMP and there can be many employees in a department.
I want to find all the departments with exactly one employee and also the sole employee's name.
How would you recommend doing it. The one way I am thinking of is to perform a self-join of DEPT_EMP with itself:
SELECT D1.DEPT, D1.EMP
  FROM DEPT_EMP D1
  LEFT JOIN DEPT_EMP D2 ON (D2.DEPT = D1.DEPT AND D1.EMP <> D2.EMP)
  WHERE D2.DEPT IS NULL;In theory it should work, but I haven't tested it. Are there other ways?
Edited by: user10936714 on Jul 1, 2009 12:44 PM

Answer 1

This will give your all the details of the employee
SQL> select * from emp
  2  where deptno in (
  3  select deptno
  4  from emp
  5  group by deptno
  6  having count(*) = 1 )
  7  /
     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
      7369 SMITH      CLERK           7902 17-DEC-80        800                    99OR
Without Using a group by clause
SQL> select ename , deptno
  2  from (
  3  select ename , deptno , count(ename) over ( partition by deptno ) k
  4  from emp  )
  5* where k =1
ENAME          DEPTNO
SMITH              99SS