Find free adjacent timeslot in postgres - sql

Question

I have a table containing timeslots for booking appointments and i try to figure out a way with a sql statement/view to find adjacent free timeslots for appointments of different duration.
The create table looks like this:
CREATE TABLE timeslot
(
timeslot_id bigserial NOT NULL,
duration bigint,
successor bigint,
predecessor bigint,
start_year character varying NOT NULL,
start_month character varying NOT NULL,
start_day character varying NOT NULL,
start_hour character varying NOT NULL,
start_minute character varying NOT NULL,
end_year character varying NOT NULL,
end_month character varying NOT NULL,
end_day character varying NOT NULL,
end_hour character varying NOT NULL,
end_minute character varying NOT NULL,
employee_id integer NOT NULL,
available_status_id integer,
appoint_calendar_id integer
CONSTRAINT timeslot_id PRIMARY KEY (timeslot_id),
CONSTRAINT appoint_calendar_id FOREIGN KEY (appoint_calendar_id)
REFERENCES appoint_calendar (appoint_calendar_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT available_status_id FOREIGN KEY (available_status_id)
REFERENCES available_status (available_status_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT employee_id FOREIGN KEY (employee_id)
REFERENCES employee (employee_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)
Here is example insert data where a available_status_id of 1 means a free timeslot
and a available_status_id of 2 is a free timeslot:
INSERT INTO timeslot(
timeslot_id, duration, successor, predecessor, start_year, start_month,
start_day, start_hour, start_minute, end_year, end_month, end_day,
end_hour, end_minute, employee_id, available_status_id, appoint_calendar_id)
VALUES (11870, 30, null, 11869, "2013", "09",
"02", "18", "00", "2013", "09", "02",
"18", "30", 4, 1, null);
INSERT INTO timeslot(
timeslot_id, duration, successor, predecessor, start_year, start_month,
start_day, start_hour, start_minute, end_year, end_month, end_day,
end_hour, end_minute, employee_id, available_status_id, appoint_calendar_id)
VALUES (11904, 30, 12000, 11999, "2013", "09",
"09", "10", "30", "2013", "09", "09",
"11", "00", 5, 2, 761);
I am looking for a query in postgres to find all free timeslots for appointments of different durations like 15, 30 or 60 minutes. At the moment I just get all free timeslots from the database and iterate over them in Java and add together the minutes of duration until I have found enough adjacent timeslots and return then the first timeslot for each subgroup to be displayed in a calendar. But there must be a better and quicker way in postgres?
Thanks in advance
Edit
Input is the needed duration in minutes (e.g 60), the employee_id (e.g. 5) and a date (e.g. 09.09.2013).
Required output are all subsets that are adjacent (in time), free and have enough duration.
For the above example this could be:
timeslot_id 11904
duration 30
successor 12000
predecessor 11999
start_year 2013
start_month 09
start_day 09
start_hour 10
start_minute 30
end_year 2013
end_month 09
end_day 09
end_hour 11
end_minute 00
employee_id 5
available_status_id 1
appoint_calendar_id null
and
timeslot_id 12000
duration 30
successor 11906
predecessor 11904
start_year 2013
start_month 09
start_day 09
start_hour 11
start_minute 00
end_year 2013
end_month 09
end_day 09
end_hour 11
end_minute 30
employee_id 5
available_status_id 1
appoint_calendar_id null

Answer 1

Personally, I think it's good idea to make this in Java code.
Other option may be creating PostgreSQL function with cursor.
But if you really want to perform this in one SQL request and suppose you have timeslot_id that is differs by exactly one for each consecutive time slot and you can predict maximum appointment duration and number of time slots needed you can try something like this:
select ts1.timeslot_id as start_timeslot_id,
coalesce(t4.timeslot_id, t3.timeslot_id, t2.timeslot_id, t1.timeslot_id) as end_timeslot_id,
coalesce(t4.end_hour, t3.end_hour, t2.end_hour, t1.end_hour)*60+coalesce(t4.end_minute, t3.end_minute, t2.end_minute, t1.end_minute) - t1.start_hour*60+t1.start_minute as duration_minutes
from timeslot ts1
left join timeslot ts2
on ts1.timeslot_id+1 = ts2.timeslot_id
and t12.available_status_id = 1
left join timeslot ts3
on ts2.timeslot_id+1 = ts3.timeslot_id
and ts3.available_status_id = 1
left join timeslot ts4
on ts3.timeslot_id+1 = ts4.timeslot_id
and ts4.available_status_id = 1
where ts1.start_year = '2013' -- these all are your input parameters
and ts1.start_month = '09'
and ts1.start_day = '09'
and employee_id = 5
and coalesce(t4.end_hour, t3.end_hour, t2.end_hour, t1.end_hour)*60+coalesce(t4.end_minute, t3.end_minute, t2.end_minute, t1.end_minute) - t1.start_hour*60+t1.start_minute >= 60 -- duration in minutes
Presumably, this request will give you every possible time slots that are bigger or equals to required one.
I didn't try to run this query against real database, so it might contain errors.

Answer 2

CREATE TABLE appoint_calendar ( appoint_calendar_id SERIAL NOT NULL PRIMARY KEY);
INSERT INTO appoint_calendar(appoint_calendar_id) VALUES (761),(762);
CREATE TABLE employee (employee_id SERIAL NOT NULL PRIMARY KEY);
INSERT INTO employee(employee_id) VALUES (4),(5);
CREATE TABLE available_status (available_status_id SERIAL NOT NULL PRIMARY KEY);
INSERT INTO available_status(available_status_id) VALUES (1),(2);
CREATE TABLE timeslot
( timeslot_id bigserial NOT NULL PRIMARY KEY
, duration bigint
, successor bigint
, predecessor bigint
, start_date timestamp with time zone
, end_date timestamp with time zone
, employee_id integer NOT NULL
REFERENCES employee (employee_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
, available_status_id integer
REFERENCES available_status (available_status_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
, appoint_calendar_id integer
REFERENCES appoint_calendar (appoint_calendar_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
);
INSERT INTO timeslot(timeslot_id, duration,successor,predecessor,start_date,end_date,employee_id,available_status_id,appoint_calendar_id) VALUES
(11870, 30, null, 11869, '2013-09-02 18:00:00', '2013-09-02 18:30:00', 4, 1, null)
, (11904, 30, 12000, 11999, '2013-09-09 10:30:00', '2013-09-09 11:00:00', 5, 2, 761)
;
Select some timeslots (the interval arithmetic is not entirely correct, YMMV)
SELECT * FROM timeslot ts
WHERE ts.employee_id IN(5)
AND ts.available_status_id IN(1, 2)
AND ts.start_date::date = '2013-09-09'::date
AND ts.end_date >= (ts.start_date + '30 min'::interval)
;