Use 'group by' on one column but get data of multiple columns - sql

Question

How can you manage to make a 'group by' on one column and still get data (the real data, not a 'sum') on the others?
Let me show an example of what I'd like to do:
Suppose Table A, with index on 'Group', a simple select * from A gives:
Group Album
---------------- ---------------
ABBA Waterloo
AC/DC Back in Black
ABBA Voulez-vous
ABBA Super Trooper
Imagine Dragons Night Visions
AC/DC Highway to Hell
ABBA The Visitors
I'd like to have the end result as following (knowing that I cannot have more than 4 albums for a group ... for now I guess):
Group Album1 Album2 Album3 Album4
---------------- --------------- --------------- --------------- ---------------
ABBA Waterloo Voulez-vous Super Trooper The visitors
AC/DC Back in Black Highway to Hell Null Null
Imagine Dragons Night Visions Null Null Null
So far, the closest I've come to make what I want is something like the following:
select tab4.GROUP,
tab1.ALBUM as PN1,
tab2.ALBUM as PN2,
tab3.ALBUM as PN3,
tab4.ALBUM as PN4
from
(
select A.GROUP, A.ALBUM
from A
where A.ROWID in
(select max(ROWID) from A
where GROUP in (select GROUP from A A group by A.GROUP having count(*) <= 4)
group by GROUP
)
) tab4
left join
(
select A.GROUP, A.ALBUM
from A A
where A.ROWID in
(select max(ROWID) from A
where GROUP in (select GROUP from A A group by A.GROUP having count(*) <= 3)
group by GROUP
)
) tab3 on tab4.GROUP = tab3.GROUP
left join
(
select A.GROUP, A.ALBUM
from A A
where A.ROWID in
(select max(ROWID) from A
where GROUP in (select GROUP from A A group by A.GROUP having count(*) <= 2)
group by GROUP
)
)tab2 on tab4.GROUP = tab2.GROUP
left join
(
select A.GROUP, A.ALBUM
from A A
where A.ROWID in
(select max(ROWID) from A
where GROUP in (select GROUP from A A group by A.GROUP having count(*) <= 1)
group by GROUP
)
) tab1 on tab4.GROUP = tab1.GROUP;
I know why the SQL request above is wrong: the max(rowid) will remain the same whatever condition on having count(*) is thrown.
There could be some pivotto be used, but I sincerely don't see how can it be used as I have only one table and need to get all data.
As furter precision, I don't need the have the result table in a spcific order and I can limit myself to 4 albums because I know each 'Group' won't have more than that ... but I'd appreciate something generic.
EDIT: Ok, seems I have forgotten to clarify that I'm on Oracle 10g (damn this legacy code ^^) so newer functions like PIVOT won't work.
Also, I'm not looking for a string aggregation like LISTAGG but really for separate columns.

Answer 1

#Alex Poole got it right: I was not only missing the equivalent of PIVOT code in 10g, but also ROW_NUMBER().
So the answer to my problem becomes as following:
select
tab1.group_name,
MAX(CASE WHEN tab1.rank_number = 1 THEN tab1.album_name ELSE NULL END) AS ALBUM_1,
MAX(CASE WHEN tab1.rank_number = 2 THEN tab1.album_name ELSE NULL END) AS ALBUM_2,
MAX(CASE WHEN tab1.rank_number = 3 THEN tab1.album_name ELSE NULL END) AS ALBUM_3,
MAX(CASE WHEN tab1.rank_number = 4 THEN tab1.album_name ELSE NULL END) AS ALBUM_4
from (
select group_name, album_name,
row_number() over (partition by group_name order by album_name) as rank_number
from tablea
) tab1
group by tab1.group_name;
Not sure if my title is the best for the kind of problem I had, guess I'll keep it as it is since it revolves around group by as well.

Answer 2

I believe this should work on 10i:
with r as (
select
group_,
album,
row_number() over (partition by group_ order by album) r
from
tq84_table_a
)
select
r.group_,
max(case when r.r=1 then r.album end) album1,
max(case when r.r=2 then r.album end) album2,
max(case when r.r=3 then r.album end) album3,
max(case when r.r=4 then r.album end) album4
from
r
group by
r.group_;
I don't have a 10i installation at hand, right now, so I can't test it.