Question

Given three tables Ta, Tb, Tc:

Ta(ID, Field1)
Tb(ID, Field2)
Tc(ID, Field3)

Given data example:

Ta
ID Field1
---------
1  A
1  B

Tb
ID Field2
---------
1  C
1  D
2  E

Tc
ID Field3
---------
1  F
2  G
2  H

Question:
How can I join this data to return:

ID Field1 Field2 Field3
-----------------------
1  A      C      F
1  B      D      NULL
2  NULL   E      G
2  NULL   NULL   H

I thought I could achieve this with outer joins but that doesn’t seem to be the case. The order of the groupings doesn’t really matter, as long as I bring back all information without duplicate rows.

Just to clarify. I don’t really mind which combination I get as long as the result set returns all data in the minimum number of rows. Here’s a more realistic example of what I am trying to do:

Given a person, call him John. He has two phone numbers and three email addresses:

PID  Email
---------
John [e-mail]
John [e-mail]
John [e-mail]

PID  Tel
--------
John 011
John 022

I want to return:

PID  Email         Tel
----------------------
John [e-mail] 011
John [e-mail] 022
John [e-mail] NULL

Answer 1

You can come close with the following:

select coalesce(ta.id, tb.id, tc.id), ta.field1, tb.field2, tc.field3
from (select ta.*, row_number() over (partition by id order by (select NULL)) as seqnum
      from ta
     ) ta full outer join
     (select tb.*, row_number() over (partition by id order by (select NULL)) as seqnum
      from tb
     ) tb
     on ta.id = tb.id and
        ta.seqnum = tb.seqnum
     (select tc.*, row_number() over (partition by id order by (select NULL)) as seqnum
      from tc
     ) tc
     on coalesce(ta.id, tb.id) = tc.id and
        coalesce(ta.seqnum, tb.seqnum) = tc.seqnum
group by coalesce(ta.id, tb.id, tc.id),
         coalesce(ta.seqnum, tb.seqnum, tc.seqnum)
order by 1, 2

As I said, though, in my comment, the ordering of rows in a table is not guaranteed, so these may not come out in the order you expect. With your sample data, you could use:

over (partition by id order by field<n>)

If the fields define the ordering