Random TIMESTAMP out of range - oracle

Question

I'm trying to create a function, which returns a random TIMESTAMP between a range of timestamps.
It doesn't appear to be working ALL the time as sometimes I get a value back before the starting range and sometimes I get a value back after the ending range.
Below is my test CASE and example of a TIMESTAMP out of range.In this example the TIMESTAMP is after the ending range of TIMESTAMP '2023-01-25 12:00:00'
Can someone please explain what the problem is and show me how to fix it as I can't seem to figure this out.
ALTER SESSION SET NLS_TIMESTAMP_FORMAT = 'DD-MON-YYYY HH24:MI:SS.FF';
CREATE OR REPLACE FUNCTION random_timestamp(
p_from IN TIMESTAMP,
p_to IN TIMESTAMP,
p_fraction IN VARCHAR2 DEFAULT 'Y'
) RETURN TIMESTAMP
IS
return_val_y TIMESTAMP := p_from + dbms_random.value () * (p_to - p_from + INTERVAL '1' DAY);
return_val_n TIMESTAMP (0) := return_val_y;
BEGIN
RETURN CASE
WHEN UPPER (SUBSTR (p_fraction, 1, 1)) = 'Y'
THEN return_val_y
ELSE return_val_N
END;
END random_timestamp;
/
SELECT random_timestamp(
TIMESTAMP '2023-01-25 09:00:00', TIMESTAMP '2023-01-25 12:00:00') as ts from dual
TS
26-JAN-2023 03:59:06.013730

Answer 1

You are adding 1 day:
p_from + dbms_random.value () * (p_to - p_from + INTERVAL '1' DAY);
It falls within the range of p_from to p_to plus 1 day and is doing exactly what you told it to do.
If you don't want the range to be 1 day extra then remove + INTERVAL '1' DAY
CREATE OR REPLACE FUNCTION random_timestamp(
p_from IN TIMESTAMP,
p_to IN TIMESTAMP,
p_fraction IN VARCHAR2 DEFAULT 'Y'
) RETURN TIMESTAMP
IS
return_val_y TIMESTAMP(9) := p_from + dbms_random.value() * (p_to - p_from);
return_val_n TIMESTAMP(0) := return_val_y;
BEGIN
RETURN CASE
WHEN p_fraction LIKE 'Y%' OR p_fraction LIKE 'y%'
THEN return_val_y
ELSE return_val_n
END;
END random_timestamp;
/
Then:
SELECT MIN(ts),
MAX(ts)
FROM (
SELECT random_timestamp(
TIMESTAMP '2023-01-25 09:00:00',
TIMESTAMP '2023-01-25 12:00:00'
) AS ts
FROM DUAL
CONNECT BY LEVEL <= 1e6
);
May randomly output:
MIN(TS)
MAX(TS)
25-JAN-23 09.00.00.017186000
25-JAN-23 11.59.59.999534000
And stays within the range.
fiddle