Oracle recursive CTE for date with interval - sql

Question

I'm trying to create a recursive CTE, which generates a date/time for every 10 minutes and stops at midnight but I am struggling with the syntax and can't seem to get it to work.
I would be very appreciative to anyone who can help me out. Thanks in advance to all who answer.
ALTER SESSION SET NLS_DATE_FORMAT = 'MMDDYYYY HH24:MI:SS';
with date_rows
(( SELECT TO_DATE('2021/08/20 18:30:25', 'YYYY/MM/DD HH24:MI:SS') as start_date FROM DUAL )
union all
select start_date+interval '10' minute
from date_rows
where start_date <
TRUNC(start_date) + INTERVAL '1' DAY)
select * from date_rows;

Answer 1

You can use:
WITH inputs ( value ) AS (
SELECT TO_DATE('2021/08/20 18:30:25', 'YYYY/MM/DD HH24:MI:SS')
FROM DUAL
),
date_rows ( start_date, end_date ) AS (
SELECT value,
TRUNC(value) + INTERVAL '1' DAY
FROM inputs
UNION ALL
SELECT start_date + INTERVAL '10' MINUTE,
end_date
FROM date_rows
WHERE start_date + INTERVAL '10' MINUTE < end_date
)
SELECT start_date
FROM date_rows;
or, if you want to duplicate the input value then you can use:
WITH date_rows ( start_date ) AS (
SELECT TO_DATE('2021/08/20 18:30:25', 'YYYY/MM/DD HH24:MI:SS')
FROM DUAL
UNION ALL
SELECT start_date + INTERVAL '10' MINUTE
FROM date_rows
WHERE start_date + INTERVAL '10' MINUTE
< TRUNC(TO_DATE('2021/08/20 18:30:25', 'YYYY/MM/DD HH24:MI:SS'))
+ INTERVAL '1' DAY
)
SELECT *
FROM date_rows;
Note: At each iteration of the recursive sub-query, start_date is the previous value so you need to check if start_date + INTERVAL '10' MINUTE is before midnight (rather than just start_date) otherwise you will have the final row after midnight.
db<>fiddle here
What was wrong with your code:
For a non-recursive sub-query factoring clause, the syntax is:
WITH query_alias AS (
or
WITH query_alias (column_alias) AS (
You were missing the AS keyword.
However, for a recursive sub-query factoring clause, you need to use the second version and specify the column aliases.
The () brackets around the first SELECT are redundant (but won't cause an error).
start_date < TRUNC(start_date) + INTERVAL '1' DAY) is always going to be true, even if the date goes past the midnight boundary; so the query will recurse infinitely.
db<>fiddle here

Answer 2

Something like this, I presume.
SQL> with date_rows (datum) as
2 (select cast (to_date('2021/08/20 18:30:25', 'YYYY/MM/DD HH24:MI:SS') as date)
3 from dual
4 union all
5 select cast (datum + interval '10' minute as date)
6 from date_rows
7 where datum < trunc(to_date('2021/08/20 18:30:25', 'YYYY/MM/DD HH24:MI:SS')) + interval '1' day
8 )
9 select * from date_rows;
DATUM
-----------------
08202021 18:30:25
08202021 18:40:25
08202021 18:50:25
08202021 19:00:25
08202021 19:10:25
08202021 19:20:25
08202021 19:30:25
08202021 19:40:25
08202021 19:50:25
08202021 20:00:25
08202021 20:10:25
<snip>
08202021 23:20:25
08202021 23:30:25
08202021 23:40:25
08202021 23:50:25
08212021 00:00:25
34 rows selected.
SQL>