Union merging different columns - sql

Question

I have two tables:
Table1:
DATAID| NAME | FACTOR
1 | Ann | 1
2 | Kate | 1
3 | Piter | 1
Table2:
DATAID| NAME | FACTOR
1 | John | 2
6 | Arse | 2
3 | Garry | 2
I would like UNION those tables and get this result:
DATAID| NAME | FACTOR
1 | Ann | 1,2
2 | Kate | 1
3 | Piter | 1,2
6 | Arse | 2
So when there's 2 rows with same dataid, I would like to get 'NAME' column from Table1 and some kind of aggregated FACTOR, for example '1,2' or 3

Answer 1

One method uses listagg():
select dataid, name,
listagg(factor, ',') within group (order by factor) as factors
from ((select dataid, name, factor from table1 t1
) union all
(select dataid, name, factor from table2 t2
)
) t
group by dataid, name;
Note: I notice that the names are not the same for a given id. You can choose one by using aggregation functions.
Or, if you only have one row in each table, you can use a full outer join:
select coalesce(t1.dataid, t2.dataid) as dataid,
coalesce(t1.name, t2.name) as name,
trim(leading ',' from coalesce(',' || t1.factor, ',') || coalesce(',' || t2.factor, '') as factors
from t1 full outer join
t2
on t1.dataid = t2.dataid;

Answer 2

Something like this should work. In your actual situation you will not need the first two CTE's (the subqueries in the WITH clause I added for testing).
with
table1 ( dataid, name, factor ) as (
select 1, 'Ann' , 1 from dual union all
select 2, 'Kate' , 1 from dual union all
select 3, 'Piter', 1 from dual
),
table2 ( dataid, name, factor ) as (
select 1, 'John' , 2 from dual union all
select 6, 'Arse' , 2 from dual union all
select 3, 'Garry', 2 from dual
),
u ( dataid, name, factor, source ) as (
select dataid, name, factor, 1 from table1
union all
select dataid, name, factor, 2 from table2
),
z ( dataid, name, factor ) as (
select dataid, first_value(name) over (partition by dataid order by source),
factor
from u
)
select dataid, name,
listagg(factor, ',') within group (order by factor) as factor
from z
group by dataid, name
order by dataid
;
Output:
DATAID NAME FACTOR
------- ----- ---------
1 Ann 1,2
2 Kate 1
3 Piter 1,2
6 Arse 2
4 rows selected.