oracle sql query months - sql

Question

I'm fairly new to SQL and I have a question regarding a query.
I would like to use a "with-clause" to create a temporary table that displays all months between two dates.
I will then use this temporary table to apply a filter to my actual table.
My query:
WITH monlist(mon, next_mon) as (
select add_months(trunc(to_date(:P6_DATUM_VON,'DD-MM-YYYY'), 'MM'), level - 1), add_months(trunc(to_date(:P6_DATUM_VON,'DD-MM-YYYY'), 'MM'), level)
from dual
connect by level <= (months_between(to_date(:P6_DATUM_BIS,'DD-MM-YYYY'), to_date(:P6_DATUM_VON,'DD-MM-YYYY')))
The problem is that I want to narrow it down to days, i.e. if I want to start from 05-01-2022 (DD-MM-YYY), this is not possible.
The temporary table starts with the beginning of the month (01-01-2022).
It is similar with the end - it is rounded up to the full month.
Is there a way to change the query so that the initial and final values are accepted correctly?
I would like to get the following output:
mon next_mon
05-01.2022 - 01-02-2022
01-02-2022 - 28-02-2022
...
01-10-2022 - 15-10-2022 (If end-date is 15-10-2022)

Answer 1

If it were PL/SQL, you'd use IF-THEN-ELSE; in SQL, use CASE expression. Something like this (example ran in SQL*Plus, hence substitution variables):
SQL> alter session set nls_date_format = 'dd-mm-yyyy';
Session altered.
SQL> set ver off
SQL>
SQL> WITH monlist as
2 (select add_months(trunc(to_date('&&P6_DATUM_VON','DD-MM-YYYY'), 'MM'), level - 1) mon,
3 add_months(trunc(to_date('&&P6_DATUM_VON','DD-MM-YYYY'), 'MM'), level) next_mon,
4 level lvl
5 from dual
6 connect by level <= months_between(to_date('&&P6_DATUM_BIS','DD-MM-YYYY'),
7 to_date('&&P6_DATUM_VON','DD-MM-YYYY')
8 ) + 1
9 )
10 select case when lvl = 1
11 then to_date('&&P6_DATUM_VON','DD-MM-YYYY') else mon end mon,
12 case when lvl = (select max(lvl) from monlist)
13 then to_date('&&P6_DATUM_BIS','DD-MM-YYYY') else next_mon end next_mon
14 from monlist
15 order by lvl;
Enter value for p6_datum_von: 05-01-2022
Enter value for p6_datum_bis: 15-10-2022
MON NEXT_MON
---------- ----------
05-01-2022 01-02-2022
01-02-2022 01-03-2022
01-03-2022 01-04-2022
01-04-2022 01-05-2022
01-05-2022 01-06-2022
01-06-2022 01-07-2022
01-07-2022 01-08-2022
01-08-2022 01-09-2022
01-09-2022 01-10-2022
01-10-2022 15-10-2022
10 rows selected.
SQL>
In Apex (you do use it, right? Regarding :P6_... item names?), that would be just
WITH monlist as
(select add_months(trunc(to_date(:P6_DATUM_VON,'DD-MM-YYYY'), 'MM'), level - 1) mon,
add_months(trunc(to_date(:P6_DATUM_VON,'DD-MM-YYYY'), 'MM'), level) next_mon,
level lvl
from dual
connect by level <= months_between(to_date(:P6_DATUM_BIS,'DD-MM-YYYY'),
to_date(:P6_DATUM_VON,'DD-MM-YYYY')
) + 1
)
select case when lvl = 1
then to_date(:P6_DATUM_VON,'DD-MM-YYYY') else mon end mon,
case when lvl = (select max(lvl) from monlist)
then to_date(:P6_DATUM_BIS,'DD-MM-YYYY') else next_mon end next_mon
from monlist
order by lvl;