Confused about the join output

Question

This one shows employee and there manager
select e.last_name employee ,e.hire_date,s.last_name manager ,s.hire_date
from employees e , employees s
where e.manager_id=s.employee_id
Dont know what it shows
select e.last_name employee ,e.hire_date,s.last_name manager ,s.hire_date
from employees e , employees s
where[b] s.manager_id = e.employee_id
If I cange manager_id , employee_id's table ..result are different ...I do not
understand Why ?
please help.

Answer 1

example:
If we take your first query (the one that's correct) and order it by the employee surname we get (let's just look at the first few rows)...
SQL> ed
Wrote file afiedt.buf
  1  select emp.last_name employee, emp.hire_date, mgr.last_name manager, mgr.hire_date
  2  from employees emp, employees mgr
  3  where emp.manager_id=mgr.employee_id
  4* order by emp.last_name
SQL> /
EMPLOYEE                  HIRE_DATE MANAGER                   HIRE_DATE
Abel                      11-MAY-96 Zlotkey                   29-JAN-00
Ande                      24-MAR-00 Errazuriz                 10-MAR-97
Atkinson                  30-OCT-97 Fripp                     10-APR-97
Austin                    25-JUN-97 Hunold                    03-JAN-90
Baer                      07-JUN-94 Kochhar                   21-SEP-89
Baida                     24-DEC-97 Raphaely                  07-DEC-94
Banda                     21-APR-00 Errazuriz                 10-MAR-97
Bates                     24-MAR-99 Cambrault                 15-OCT-99Now if we take your second query and this time order it by the manager last_name (again looking at the first few rows)...
SQL> ed
Wrote file afiedt.buf
  1  select emp.last_name employee, emp.hire_date, mgr.last_name manager, mgr.hire_date
  2  from employees emp, employees mgr
  3  where mgr.manager_id=emp.employee_id
  4* order by mgr.last_name
SQL> /
EMPLOYEE                  HIRE_DATE MANAGER                   HIRE_DATE
Zlotkey                   29-JAN-00 Abel                      11-MAY-96
Errazuriz                 10-MAR-97 Ande                      24-MAR-00
Fripp                     10-APR-97 Atkinson                  30-OCT-97
Hunold                    03-JAN-90 Austin                    25-JUN-97
Kochhar                   21-SEP-89 Baer                      07-JUN-94
Raphaely                  07-DEC-94 Baida                     24-DEC-97
Errazuriz                 10-MAR-97 Banda                     21-APR-00
Cambrault                 15-OCT-99 Bates                     24-MAR-99You can see that the data is the same but you have transposed the employee details into the manager columns and the manager details into the employee columns.