Single row from one-to-many

Question

I am having trouble with a query, I need a single row from a 1-to-many relationship that is prioritized by certain ID's.
Department Table - dept_id,dept_name
Employee Table - emp_id, emp_name
D-E-Lookup Table - dept_id,emp_id
Employee ID priority are 5,8,9,21,33,78
I need each department name with the associated employee name.
There should be only one row per department.
If that department does not have empID 5, than 8, if not 8 then 9, if not 9 than 21, etc
Any help would be greatly appreciated.

Answer 1

How about this:
WITH departments AS
    ( SELECT ROWNUM AS deptno, COLUMN_VALUE AS dname
      FROM   TABLE(sys.dbms_debug_vc2coll('Sales','IT','Research')) )
   , employees AS
    ( SELECT ROWNUM AS empno, COLUMN_VALUE AS ename
      FROM   TABLE(sys.dbms_debug_vc2coll('Bennett','Parkman','Nakamura')) )
   , department_assignments AS
     ( SELECT 1 AS deptno, 1 AS empno, 5 AS priority FROM dual UNION ALL
       SELECT 1 AS deptno, 2 AS empno, 8 AS priority FROM dual UNION ALL
       SELECT 1 AS deptno, 3 AS empno, 9 AS priority FROM dual UNION ALL
       SELECT 2 AS deptno, 2 AS empno, 8 AS priority FROM dual UNION ALL
       SELECT 2 AS deptno, 3 AS empno, 9 AS priority FROM dual UNION ALL
       SELECT 3 AS deptno, 1 AS empno, 9 AS priority FROM dual UNION ALL
       SELECT 3 AS deptno, 3 AS empno, 21 AS priority FROM dual )
SELECT dname, ename, priority
FROM   ( SELECT d.dname
              , e.ename
              , dp.priority
              , DENSE_RANK() OVER (PARTITION BY d.deptno ORDER BY dp.priority) AS ranking
         FROM   departments d
                LEFT JOIN department_assignments dp ON dp.deptno = d.deptno
                LEFT JOIN employees e ON e.empno = dp.empno )
WHERE ranking = 1;
DNAME         ENAME             PRIORITY
Sales         Bennett                  5
IT            Parkman                  8
Research      Bennett                  9
3 rows selectedThe <tt>WITH</tt> clause is just to define test data inline rather than creating tables, in case that's not clear.