Confusion in group by function- Any thoughts?

Question

Hi,
I always have a doubt regarding the group by function i.e. if we are using a group by function and we want to display some columns which are not to be grouped by then how do we display those.
Like for eg.
to display last name, department no and average of salary for each department how should we proceed.
I know we can display the department no, and avg(sal) but how abt the last name.
Do we use a subquery?
Any thoughts or explanaitions with example?
Thanks

Answer 1

While the analytic functions already suggested are likely more efficient for y our example, there are cases where they may not be. An alternative formulation without analytics would be something like:
SQL> SELECT s.department_id, e.last_name, s.average
  2  FROM (SELECT department_id, AVG(salary) average
  3        FROM employees
  4        GROUP BY department_id) s, employees e
  5  WHERE s.department_id = e.department_id
  6  ORDER BY s.department_id;
DEPARTMENT_ID LAST_NAME                    AVERAGE
           10 Whalen                          4400
           20 Hartstein                       9500
           20 Fay                             9500
           30 Raphaely                        4150
           30 Tobias                          4150
           30 Colmenares                      4150
           30 Himuro                          4150
           30 Baida                           4150
           30 Khoo                            4150
           40 Mavris                          6500
           50 Taylor                    3475.55556
           50 Fleaur                    3475.55556
           50 Sullivan                  3475.55556
           50 Geoni                     3475.55556
           50 Cabrio                    3475.55556HTH
John