Update Oracle SQL - table with values from duplicates - sql

Question

i hope that somebody could help. I need to update a table from a select with duplicates.
ID;CLASS;VALUE;NEW
1;a;a3;
1;b;s6;
1;c;b99;
2;a;s3;
2;b;r6;
2;c;b99;
3;a;s5;
4;a;r6;
4;b;a3;
Look at my example table, there is a colum NEW which i have to update. In the example the column NEW was filled manually.
Here is the goal (as shown in table col NEW):
1.find duplicates via ID (HAVING COUNT(*) >1 or something like that)
UPDATE TABLE SET NEW=
CLASS || '_' || VALUE
WHERE CLASS='a' or 'b'
Easy for you?
Thx in advance

Answer 1

The logic behind is not completely clear; this could be a way.
setup:
create table yourTable(id, class, value, new) as
(
select 1, 'a', 'a3', cast (null as varchar2(10)) from dual union all
select 1, 'b', 's6', null from dual union all
select 1, 'c', 'b99', null from dual union all
select 2, 'a', 's3', null from dual union all
select 2, 'b', 'r6', null from dual union all
select 2, 'c', 'b99', null from dual union all
select 3, 'a', 's5', null from dual union all
select 4, 'a', 'r6', null from dual union all
select 4, 'b', 'a3', null from dual
)
query:
merge into yourTable t1
using (
select listagg(value, '_') within group (order by class) as new,
id
from yourTable
where class in ('a', 'b')
group by id
having count(distinct class) = 2
) t2
on ( t1.id = t2.id
and t1.class in ('a', 'b')
)
when matched then
update set t1.new = t2.new
result:
SQL> select *
2 from yourTable;
ID C VAL NEW
---------- - --- ----------
1 a a3 a3_s6
1 b s6 a3_s6
1 c b99
2 a s3 s3_r6
2 b r6 s3_r6
2 c b99
3 a s5
4 a r6 r6_a3
4 b a3 r6_a3
9 rows selected.