Concatenation of max_times within 15 minute time intervals SQL - sql

Question

I am trying to write a sql query that pulls an ID and concatenates the max times within 15 minute time intervals starting from the first time.
i.e. for one log_id data might be
101 01:01
101 01:08
101 01:23
101 02:01
101 02:10
101 02:16
we would want to display
101 01:01, 01:08, 01:23, 2:01, 2:16
any ideas?
here is the starting query we are using:
select
ol.log_id,
ifm.meas_value,
ifm.measure_id,
ifm.recorded_time
from meas ifm
inner join rec ifr on ifm.fsd_id = ifr.fsd_id
inner join pe on ifr.data_id = pe.data_id
inner join record_summary f on pe.n_id = f.n_id
inner join pe2 on pe.t_id = pe2.t_id and pe.date = pe2.date and pe2.type = 51
inner join log l on pe2.ata_id = l.data_id and l.date = pe2.date
where ifm.measure_id in ('891')
and ol.date >= trunc(sysdate - 3)
for each log_id there will be multiple recorded times we want to pull the first time, and the maximum time in every 15 minute interval until the last time. These times will be concatenated to a list.
We tried a listagg with all the values, but there are too many times so the end-user wants to only see one value for every 15 minutes.

Answer 1

Basically you have 3 questions in one:
How to round date field to 15 min?
https://community.oracle.com/thread/1042863
ceil(to_number(to_char(test_timestamp, 'yyyymmddhh24mi'))/15) * 15
How to get the row from a group?
That is a very popular question, you will find something here:
https://stackoverflow.com/questions/tagged/oracle+greatest-n-per-group?sort=votes&pageSize=30
How to aggregate over string values to concatenate within a group:
LISTAGG(convertedTimeField, ' ')
Try to combine all three pieces in one query to get required result.

Answer 2

To simplify working with the following table:
CREATE TABLE Test ( id NUMBER, log DATE );
(Note: DATE in oracle is actually dateTime. String concatenation is done with ||.)
Your given list seems to indicate, that when the max and the min is the same you only display it once, this can be done by grouping twice:
SELECT
O.id,
O.logDate,
LISTAGG(O.logTimes, ', ') WITHIN GROUP (ORDER BY O.logTimes) logTimes
FROM (
SELECT
O.id,
O.logDate,
O.G G,
CASE
WHEN TO_CHAR(MIN(O.log), 'HH24:MI') <> TO_CHAR(MAX(O.log), 'HH24:MI') THEN
TO_CHAR(MIN(O.log), 'HH24:MI') || ', ' || TO_CHAR(MAX(O.log), 'HH24:MI')
ELSE
TO_CHAR(MIN(O.log), 'HH24:MI')
END logTimes
FROM (
SELECT
T.id,
T.log,
TRUNC(T.log) logDate,
TO_CHAR(T.log, 'HH24') || FLOOR(TO_NUMBER(TO_CHAR(T.log, 'MI')) / 15) G
FROM
Test T
) O
GROUP BY
O.id, O.logDate, O.G
) O
GROUP BY
O.id, O.logDate
;
See SQL fiddle.