oracle sql how combine column string value

Question

i have records

id | key | string column
------------------------
1  | 1   | A
------------------------
1  | 1   | B
------------------------
1  | 1   | C

i want result like below

id | key | string column
------------------------
1  | 1   | A, B, C
------------------------

someone know how to do? thank you

Answer 1

You are looking for listagg() :

select id, key, listagg(string, ', ') within group (order by string)
from t
group by id, key;