Oracle 10g: Parsing 2 Columns Merging Duplicates

I'm having a table with 3 columns: DATE_A, DATE_B and ISSUE DATE_A and DATE_B can be filled in 3 possible ways: either both have a value, or only one have, as shown here: DATE_A

Solution 1:

If I understand correctly, you want a union all of the date values and string aggregation. listagg() was introduced in 11g, but you can use wm_concat():

select dte, wm_concat(issue) as issues
from ((select date_a as dte, issue from t where date_a is not null) union all
      (select date_b, issue from t where date_b is not null)
     ) di
group by dte
order by dte;