Oracle SQL query using case when, compacting null fields - sql

Question

I have a table like this:
Items
id group old_new object
1 A O pen
2 A N house
3 B O dog
4 B O cat
5 C N mars
6 C O sun
7 C N moon
8 C o earth
I would like the select return:
Items
group new_object old_object
A house pen
B null dog
B null cat
C mars sun
C moon earth
If I try:
select id,
case when old_new = 'N' then object end as new_object,
case when old_new = 'O' then object end as old_object
from the_table
order by id;
I have 8 row with many field as null
es: last rows:
group new_object old_object
C mars null
c null sun
C moon null
c null earth
But of group C I want only 2 rows...
is not like the other query 'Oracle sql join same table ecc...' because here don't want null result

Answer 1

I'm going to make the assumption that Old and New records are paired in the order they appear based on the ID value. With that assumption the following query:
WITH DTA(ID, GRP, OLD_NEW, OBJECT) AS (
select 1, 'A', 'O', 'pen' from dual union all
select 2, 'A', 'N', 'house' from dual union all
select 3, 'B', 'O', 'dog' from dual union all
select 4, 'B', 'O', 'cat' from dual union all
select 5, 'C', 'N', 'mars' from dual union all
select 6, 'C', 'O', 'sun' from dual union all
select 7, 'C', 'N', 'moon' from dual union all
select 8, 'C', 'O', 'earth' from dual
), dta2 as (
select dta.*
, row_number() over (partition by GRP, old_new order by id) rn
from dta
)
select coalesce(n.grp, o.grp) grp
, n.object new_object
, o.object old_object
from (select * from dta2 where old_new = 'N') n
full join (select * from dta2 where old_new = 'O') o
on n.grp = o.grp
and n.rn = o.rn;
Aside from the sample data section (with dta) this script first uses the analytic function ROW_NUMBER() to add a sequential number partitioned by the group and old_new columns. It then performs a full outer join on two inline views of the dta2 subfactored query, one for thr old objects and one for the new objects. The result, at least for this data set is:
GRP NEW_OBJECT OLD_OBJECT
--- ---------- ----------
A house pen
B dog
B cat
C mars sun
C moon earth

Answer 2

In the first step assign an index (IDX) of the chnage withing your group. I'm using order by ID, but this is upon you. The important thing is that the old and new valuea are unique connected with GRP and IDX.
In next step let PIVOT work for you (I'm using the data from #Sentinel, thx!)
WITH DTA(ID, GRP, OLD_NEW, OBJECT) AS (
select 1, 'A', 'O', 'pen' from dual union all
select 2, 'A', 'N', 'house' from dual union all
select 3, 'B', 'O', 'dog' from dual union all
select 4, 'B', 'O', 'cat' from dual union all
select 5, 'C', 'N', 'mars' from dual union all
select 6, 'C', 'O', 'sun' from dual union all
select 7, 'C', 'N', 'moon' from dual union all
select 8, 'C', 'O', 'earth' from dual
), DTA2 as (
SELECT
ROW_NUMBER() OVER (PARTITION BY GRP,OLD_NEW order by ID) as IDX,
GRP, OLD_NEW, OBJECT
from DTA
)
select * from DTA2
PIVOT (max(OBJECT) OBJECT for (OLD_NEW) in
('N' as "NEW",
'O' as "OLD"
))
order by GRP;
result
IDX, GRP, NEW_OBJECT, OLD_OBJECT
1 A house pen
1 B dog
2 B cat
2 C moon earth
1 C mars sun

Answer 3

Here's an alternative using PIVOT to get the results:
with items as (select 1 id, 'A' grp, 'O' old_new, 'pen' obj from dual union all
select 2 id, 'A' grp, 'N' old_new, 'house' obj from dual union all
select 3 id, 'B' grp, 'O' old_new, 'dog' obj from dual union all
select 4 id, 'B' grp, 'O' old_new, 'cat' obj from dual union all
select 5 id, 'C' grp, 'N' old_new, 'mars' obj from dual union all
select 6 id, 'C' grp, 'O' old_new, 'sun' obj from dual union all
select 7 id, 'C' grp, 'N' old_new, 'moon' obj from dual union all
select 8 id, 'C' grp, 'O' old_new, 'earth' obj from dual)
-- end of mimicking your items table with data in it. See SQL below:
select grp,
new_object,
old_object
from (select grp,
old_new,
obj,
row_number() over (partition by grp, old_new order by id) rn
from items)
pivot (max(obj)
for old_new in ('N' new_object,
'O' old_object))
order by grp,
rn;
GRP NEW_OBJECT OLD_OBJECT
--- ---------- ----------
A house pen
B dog
B cat
C mars sun
C moon earth

Answer 4

Provided that
there's at most one new object for each old,
there's no new object without old object, and
there's at most one old object for any group (this is not true for your sample data, but in comments you indicate you're interested in such solution as well)
a simpler query may be used than for the general case:
select
old.group as group, new.object as new_object, old.object as old_object
from
(select group, object from my_table where old_new = 'O') old
left join
(select group, object from my_table where old_new = 'N') new
on (old.group = new.group)