By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
CREATE TABLE table_name
(Customer_ID int, Offer_1 varchar(3), Offer_2 varchar(3), Offer_3 varchar(3))
;
INSERT INTO table_name
(Customer_ID, Offer_1, Offer_2, Offer_3)
VALUES
(111, 'A01', '001', 'B01'),
(222, 'A01', 'B01', '001'),
(333, 'A02', '001', 'B01')
;
with u as
(select Customer_ID, Offer_1 as Offer from table_name union all
select Customer_ID, Offer_2 as Offer from table_name union all
select Customer_ID, Offer_3 as Offer from table_name)
select distinct listagg(Offer, ',') within group(order by Offer) from u
group by Customer_ID
| 1 |
|---|
| 001,A01,B01 |
| 001,A02,B01 |