Get classroom available hours between date time range - sql

Question

I'm, using Oracle 11g and I have this problem. I couldn't come up with any ideas to solve it yet.
I have a table with occupied classrooms. What I need to find are the hours available between a datetime range. For example, I have rooms A, B and C, the table of occupied classrooms looks like this:
Classroom start end
A 10/10/2013 10:00 10/10/2013 11:30
B 10/10/2013 09:15 10/10/2013 10:45
B 10/10/2013 14:30 10/10/2013 16:00
What I need to get is something like this:
with date time range between '10/10/2013 07:00' and '10/10/2013 21:15'
Classroom avalailable_from available_to
A 10/10/2013 07:00 10/10/2013 10:00
A 10/10/2013 11:30 10/10/2013 21:15
B 10/10/2013 07:00 10/10/2013 09:15
B 10/10/2013 10:45 10/10/2013 14:30
B 10/10/2013 16:00 10/10/2013 21:15
C 10/10/2013 07:00 10/10/2013 21:15
Is there a way I can accomplish that with sql or pl/sql?

Answer 1

I was looking at a solution similar in concept at least to Wernfried's, but I think it's different enough to post as well. The start is the same idea, first generating the possible time slots, and assuming you're looking at 15-minute windows: I'm using CTEs because I think they're clearer than nested selects, particularly with this many levels.
with date_time_range as (
select to_date('10/10/2013 07:00', 'DD/MM/YYYY HH24:MI') as date_start,
to_date('10/10/2013 21:15', 'DD/MM/YYYY HH24:MI') as date_end
from dual
),
time_slots as (
select level as slot_num,
dtr.date_start + (level - 1) * interval '15' minute as slot_start,
dtr.date_start + level * interval '15' minute as slot_end
from date_time_range dtr
connect by level <= (dtr.date_end - dtr.date_start) * (24 * 4) -- 15-minutes
)
select * from time_slots;
This gives you the 57 15-minute slots between the start and end date you specified. The CTE for date_time_range isn't strictly necessary, you could put your dates straight into the time_slots conditions, but you'd have to repeat them and that then introduces a possible failure point (and means binding the same value multiple times, from JDBC or wherever).
Those slots can then be cross-joined to the list of classrooms, which I'm assuming are already in another table, which gives you 171 (3x57) combinations; and those can be compared with existing bookings - once those are eliminated you're left with the 153 15-minute slots that have no booking.
with date_time_range as (...),
time_slots as (...),
free_slots as (
select c.classroom, ts.slot_num, ts.slot_start, ts.slot_end,
lag(ts.slot_end) over (partition by c.classroom order by ts.slot_num)
as lag_end,
lead(ts.slot_start) over (partition by c.classroom order by ts.slot_num)
as lead_start
from time_slots ts
cross join classrooms c
left join occupied_classrooms oc on oc.classroom = c.classroom
and not (oc.occupied_end <= ts.slot_start
or oc.occupied_start >= ts.slot_end)
where oc.classroom is null
)
select * from free_slots;
But then you have to collapse those into contiguous ranges. There are various ways of doing that; here I'm peeking at the previous and next rows to decide if a particular value is the edge of a range:
with date_time_range as (...),
time_slots as (...),
free_slots as (...),
free_slots_extended as (
select fs.classroom, fs.slot_num,
case when fs.lag_end is null or fs.lag_end != fs.slot_start
then fs.slot_start end as slot_start,
case when fs.lead_start is null or fs.lead_start != fs.slot_end
then fs.slot_end end as slot_end
from free_slots fs
)
select * from free_slots_extended
where (fse.slot_start is not null or fse.slot_end is not null);
Now we're down to 12 rows. (The outer where clause eliminates all 141 of the 153 slots from the previous step which are mid-range, since we only care about the edges):
CLASSROOM SLOT_NUM SLOT_START SLOT_END
--------- ---------- ---------------- ----------------
A 1 2013-10-10 07:00
A 12 2013-10-10 10:00
A 19 2013-10-10 11:30
A 57 2013-10-10 21:15
B 1 2013-10-10 07:00
B 9 2013-10-10 09:15
B 16 2013-10-10 10:45
B 30 2013-10-10 14:30
B 37 2013-10-10 16:00
B 57 2013-10-10 21:15
C 1 2013-10-10 07:00
C 57 2013-10-10 21:15
So those represent the edges, but on separate rows, and a final step combines them:
...
select distinct fse.classroom,
nvl(fse.slot_start, lag(fse.slot_start)
over (partition by fse.classroom order by fse.slot_num)) as slot_start,
nvl(fse.slot_end, lead(fse.slot_end)
over (partition by fse.classroom order by fse.slot_num)) as slot_end
from free_slots_extended fse
where (fse.slot_start is not null or fse.slot_end is not null)
Or putting all that together:
with date_time_range as (
select to_date('10/10/2013 07:00', 'DD/MM/YYYY HH24:MI') as date_start,
to_date('10/10/2013 21:15', 'DD/MM/YYYY HH24:MI') as date_end
from dual
),
time_slots as (
select level as slot_num,
dtr.date_start + (level - 1) * interval '15' minute as slot_start,
dtr.date_start + level * interval '15' minute as slot_end
from date_time_range dtr
connect by level <= (dtr.date_end - dtr.date_start) * (24 * 4) -- 15-minutes
),
free_slots as (
select c.classroom, ts.slot_num, ts.slot_start, ts.slot_end,
lag(ts.slot_end) over (partition by c.classroom order by ts.slot_num)
as lag_end,
lead(ts.slot_start) over (partition by c.classroom order by ts.slot_num)
as lead_start
from time_slots ts
cross join classrooms c
left join occupied_classrooms oc on oc.classroom = c.classroom
and not (oc.occupied_end <= ts.slot_start
or oc.occupied_start >= ts.slot_end)
where oc.classroom is null
),
free_slots_extended as (
select fs.classroom, fs.slot_num,
case when fs.lag_end is null or fs.lag_end != fs.slot_start
then fs.slot_start end as slot_start,
case when fs.lead_start is null or fs.lead_start != fs.slot_end
then fs.slot_end end as slot_end
from free_slots fs
)
select distinct fse.classroom,
nvl(fse.slot_start, lag(fse.slot_start)
over (partition by fse.classroom order by fse.slot_num)) as slot_start,
nvl(fse.slot_end, lead(fse.slot_end)
over (partition by fse.classroom order by fse.slot_num)) as slot_end
from free_slots_extended fse
where (fse.slot_start is not null or fse.slot_end is not null)
order by 1, 2;
Which gives:
CLASSROOM SLOT_START SLOT_END
--------- ---------------- ----------------
A 2013-10-10 07:00 2013-10-10 10:00
A 2013-10-10 11:30 2013-10-10 21:15
B 2013-10-10 07:00 2013-10-10 09:15
B 2013-10-10 10:45 2013-10-10 14:30
B 2013-10-10 16:00 2013-10-10 21:15
C 2013-10-10 07:00 2013-10-10 21:15
SQL Fiddle.

Answer 2

It is always a challenge when you like to "select something which does not exist". First you need a list of all available classrooms and times (in interval of 15 Minutes). Then you can select them by skipping the occupied items.
I managed to make a query without any PL/SQL:
CREATE TABLE Table1
(Classroom VARCHAR2(10), start_ts DATE, end_ts DATE);
INSERT INTO Table1 VALUES ('A', TIMESTAMP '2013-01-10 10:00:00', TIMESTAMP '2013-01-10 11:30:00');
INSERT INTO Table1 VALUES ('B', TIMESTAMP '2013-01-10 09:15:00', TIMESTAMP '2013-01-10 10:45:00');
INSERT INTO Table1 VALUES ('B', TIMESTAMP '2013-01-10 14:30:00', TIMESTAMP '2013-01-10 16:00:00');
WITH all_rooms AS
(SELECT CHR(64+LEVEL) AS ROOM FROM dual CONNECT BY LEVEL <= 3),
all_times AS
(SELECT CAST(TIMESTAMP '2013-01-10 07:00:00' + (LEVEL-1) * INTERVAL '15' MINUTE AS DATE) AS TIMES, LEVEL AS SLOT
FROM DUAL
CONNECT BY TIMESTAMP '2013-01-10 07:00:00' + (LEVEL-1) * INTERVAL '15' MINUTE <= TIMESTAMP '2013-01-10 21:15:00'),
all_free_slots AS
(SELECT ROOM, TIMES, SLOT,
CASE SLOT-LAG(SLOT, 1, 0) OVER (PARTITION BY ROOM ORDER BY SLOT)
WHEN 1 THEN 0
ELSE 1
END AS NEW_WINDOW
FROM all_times
CROSS JOIN all_rooms
WHERE NOT EXISTS
(SELECT 1 FROM TABLE1 WHERE ROOM = CLASSROOM AND TIMES BETWEEN START_TS + INTERVAL '1' MINUTE AND END_TS - INTERVAL '1' MINUTE)),
free_time_windows AS
(SELECT ROOM, TIMES, SLOT,
SUM(NEW_WINDOW) OVER (PARTITION BY ROOM ORDER BY SLOT) AS WINDOW_ID
FROM all_free_slots)
SELECT ROOM,
TO_CHAR(MIN(TIMES), 'yyyy-mm-dd hh24:mi') AS free_time_start,
TO_CHAR(MAX(TIMES), 'yyyy-mm-dd hh24:mi') AS free_time_end
FROM free_time_windows
GROUP BY ROOM, WINDOW_ID
HAVING MAX(TIMES) - MIN(TIMES) > 0
ORDER BY ROOM, 2;
ROOM FREE_TIME_START FREE_TIME_END
---- ----------------------------------
A 2013-01-10 07:00 2013-01-10 10:00
A 2013-01-10 11:30 2013-01-10 21:15
B 2013-01-10 07:00 2013-01-10 09:15
B 2013-01-10 10:45 2013-01-10 14:30
B 2013-01-10 16:00 2013-01-10 21:15
C 2013-01-10 07:00 2013-01-10 21:15
In order to understand the query you can split the sub-queries from top, e.g.
WITH all_rooms AS
(SELECT CHR(64+LEVEL) AS ROOM FROM dual CONNECT BY LEVEL <= 3),
all_times AS
(SELECT CAST(TIMESTAMP '2013-01-10 07:00:00' + (LEVEL-1) * INTERVAL '15' MINUTE AS DATE) AS TIMES, LEVEL AS SLOT
FROM DUAL
CONNECT BY TIMESTAMP '2013-01-10 07:00:00' + (LEVEL-1) * INTERVAL '15' MINUTE <= TIMESTAMP '2013-01-10 21:15:00')
SELECT ROOM, TIMES, SLOT,
CASE SLOT-LAG(SLOT, 1, 0) OVER (PARTITION BY ROOM ORDER BY SLOT)
WHEN 1 THEN 0
ELSE 1
END AS NEW_WINDOW
FROM all_times
CROSS JOIN all_rooms
WHERE NOT EXISTS (SELECT 1 FROM TABLE1 WHERE ROOM = CLASSROOM AND TIMES BETWEEN START_TS + INTERVAL '1' MINUTE AND END_TS - INTERVAL '1' MINUTE)
ORDER BY ROOM, SLOT