Multiple Join over the same table

Question

Hi all,
I have a question concerning joins...
We are working with Oracle 8i.
Consider I have the following tables t_emp_team and t_emp_names
t_emp_team
emp_id1, emp_id2, emp_id3
2, 7, 9
3, 8, 6
4, 11, 3
5, 10, 9
t_emp_names
emp_id, name
2, Peter
3, Mark
4, Liz
5, Will
Now I want a join selecting all the names to the IDs.
My idea was to use a join query like this:
select
a.emp_id1,
a.emp_id2,
a.emp_id3,
b1.name,
b2.name,
b3.name
from
t_emp_team a,
t_emp_names b1,
t_emp_names b2,
t_emp_names b3
where
a.emp_id1=b1.emp_id(+) and
a.emp_id2=b2.emp_id(+) and
a.emp_id3=b3.emp_id(+)
Obviously this is not possible in Oracle as the results are not correct.
Do you have a different idea other than Subselects for each name? (The real table has 16 IDs meaning we would end up with 16 subselects)
Thanks for your help!
-Peter

Answer 1

Hi,
Obviously this is not possible in Oracle as the results
are not correct.Why do you think so ?
SQL> select
  2  a.emp_id1,
  3  a.emp_id2,
  4  a.emp_id3,
  5  b1.name,
  6  b2.name,
  7  b3.name
  8  from
  9  t_emp_team a,
10  t_emp_names b1,
11  t_emp_names b2,
12  t_emp_names b3
13  where
14  a.emp_id1=b1.emp_id(+) and
15  a.emp_id2=b2.emp_id(+) and
16  a.emp_id3=b3.emp_id(+)
17  /
&nbsp
   EMP_ID1    EMP_ID2    EMP_ID3 NAME       NAME       NAME
         4         11          3 Liz                   Mark
         3          8          6 Mark
         5         10          9 Will
         2          7          9 Peter
&nbspBut it would be correct to use normzlized form
of t_emp_team:
SQL> desc t_emp_team_n
Name                                      Null?    Type
TEAM_ID                                            NUMBER
EMP_ID                                             NUMBER
&nbsp
SQL> select * from t_emp_team_n;
&nbsp
   TEAM_ID     EMP_ID
         1          4
         1         11
         1          3
         2          3
         2          8
         2          6
         3          5
         3         10
         3          9
         4          2
         4          7
         4          9
&nbsp
12 rows selected.
&nbsp
Elapsed: 00:00:00.04
SQL> select team_id, a.emp_id, name
  2  from t_emp_team_n a, t_emp_names b
  3  where a.emp_id = b.emp_id (+)
  4  order by 1,3
  5  /
&nbsp
   TEAM_ID     EMP_ID NAME
         1          4 Liz
         1          3 Mark
         1         11
         2          3 Mark
         2          8
         2          6
         3          5 Will
         3         10
         3          9
         4          2 Peter
         4          7
         4          9
&nbsp
12 rows selected.and use the advise of William Robertson:
http://www.williamrobertson.pwp.blueyonder.co.uk/documents/one_row.html
SQL> select team_id, substr(epath,2) "ids",
  2  rtrim(substr(npath,2),',') "members"
  3  from (
  4  select team_id, max(sys_connect_by_path(emp_id,',')) epath,
  5  max(sys_connect_by_path(name,',')) npath from (
  6  select team_id, a.emp_id, name, row_number()
  7  over(partition by team_id order by name nulls last) rn
  8  from t_emp_team_n a, t_emp_names b
  9  where a.emp_id = b.emp_id (+)
10  )
11  start with rn = 1 connect by prior team_id = team_id
12  and prior rn = rn -1
13  group by team_id
14  )
15  /
&nbsp
   TEAM_ID ids                            members
         1 4,3,11                         Liz,Mark
         2 3,8,6                          Mark
         3 5,10,9                         Will
         4 2,7,9                          PeterRgds.