How to increase date by 1 month in Oracle sql - sql

Question

I want to add 1 month for loop by subscribed month to get each customers monthly payment date.
I have a table like this:
ID
REGISTER DATE
SUBSCRIBED MONTH
1
2022.01.01
3
2
2022.07.01
6
I want to have result like this:
ID
REGISTER DATE
SUBSCRIBED MONTH
MUST PAY DATE
1
2022.01.01
3
2022.01.01
1
2022.01.01
3
2022.02.01
1
2022.01.01
3
2022.03.01
2
2022.07.01
6
2022.07.01
2
2022.07.01
6
2022.08.01
2
2022.07.01
6
2022.09.01
2
2022.07.01
6
2022.10.01
2
2022.07.01
6
2022.11.01
2
2022.07.01
6
2022.12.01
Tried this, but returning duplicated.
SELECT ID, ADDMONTHS(REGISTER_DATE,LEVEL) FROM SUBLIST CONNECT BY LEVEL<=SUB_MONTH
Any help will be appreciated. Many thanks.

Answer 1

Here's one option:
Setting date format (you don't have to do that):
SQL> alter session set nls_date_format = 'yyyy.mm.dd';
Session altered.
Sample data:
SQL> with test (id, register_date, subscribed_month) as
2 (select 1, date '2022-01-01', 3 from dual union all
3 select 2, date '2022-07-01', 6 from dual
4 )
Query begins here:
5 select id, register_date, subscribed_month,
6 add_months(register_date, column_value - 1) must_pay_date
7 from test cross join table(cast(multiset(select level from dual
8 connect by level <= subscribed_month
9 ) as sys.odcinumberlist))
10 order by id, register_date, must_pay_date;
ID REGISTER_D SUBSCRIBED_MONTH MUST_PAY_D
---------- ---------- ---------------- ----------
1 2022.01.01 3 2022.01.01
1 2022.01.01 3 2022.02.01
1 2022.01.01 3 2022.03.01
2 2022.07.01 6 2022.07.01
2 2022.07.01 6 2022.08.01
2 2022.07.01 6 2022.09.01
2 2022.07.01 6 2022.10.01
2 2022.07.01 6 2022.11.01
2 2022.07.01 6 2022.12.01
9 rows selected.
SQL>

Answer 2

You can inner join your data to a subquery containing rows with numbers of months to be added:
WITH
tbl (ID, REGISTER_DATE, SUBSCRIBED_MONTH) AS
(
Select 1, DATE '2022-01-01', 3 From Dual Union All
Select 2, DATE '2022-07-01', 6 From Dual
)
SELECT t0.ID, t0.REGISTER_DATE, t0.SUBSCRIBED_MONTH,
Add_Months(t0.REGISTER_DATE, t1.MNTHS - 1) "PAY_DATE",
t1.MNTHS "PAYMENT_NO"
FROM tbl t0
INNER JOIN ( Select DISTINCT ID, LEVEL "MNTHS" From tbl Connect By LEVEL <= SUBSCRIBED_MONTH ) t1 ON(t1.ID = t0.ID)
ORDER BY t0.ID, t0.REGISTER_DATE, t1.MNTHS
Which with your sample data
WITH
tbl (ID, REGISTER_DATE, SUBSCRIBED_MONTH) AS
(
Select 1, DATE '2022-01-01', 3 From Dual Union All
Select 2, DATE '2022-07-01', 6 From Dual
)
... results as ...
ID REGISTER_DATE SUBSCRIBED_MONTH PAY_DATE PAYMENT_NO
---------- ------------- ---------------- --------- ----------
1 01-JAN-22 3 01-JAN-22 1
1 01-JAN-22 3 01-FEB-22 2
1 01-JAN-22 3 01-MAR-22 3
2 01-JUL-22 6 01-JUL-22 1
2 01-JUL-22 6 01-AUG-22 2
2 01-JUL-22 6 01-SEP-22 3
2 01-JUL-22 6 01-OCT-22 4
2 01-JUL-22 6 01-NOV-22 5
2 01-JUL-22 6 01-DEC-22 6