Finding free blocks of time in mysql and php?

Question

I have a table in mysql like this:

+------------+------------+------------+------------+ 
|     date   |   user_id  | start_hour | end_hour   | 
+-----------         


        

Answer 1

Try this query

SELECT
  a.id,
  a.start_hour,
  a.end_hour,
  TIMEDIFF(la.start_hour, a.end_hour) as `Free Time`
FROM appointment as a
  LEFT JOIN(SELECT * FROM appointment LIMIT 1,18446744073709551615) AS la
    ON la.id = a.id + 1
  LEFT JOIN (SELECT * FROM appointment) AS ra ON a.id = ra.id

This will show these results

+---------------------------------------------+
¦ id ¦ start_hour BY ¦ end_hour   | Free Time |
¦----+---------------¦------------------------|
¦  1 ¦   08:00:00    ¦  08:15:00  | 05:45:00  |
¦  2 ¦   14:00:00    ¦  14:30:00  | 02:30:00  |
¦  3 ¦   17:00:00    ¦  17:45:00  | 03:15:00  |
¦  4 ¦   21:00:00    ¦  21:00:00  | (NULL)    |
+--------------------+------------------------+ 

Also you must have the 21:00:00 in the table or you wont be able to get the last time difference. i entered 21:00:00 as start and end date in the table.

EDITED

This is modified query

SELECT
  a.id,
  a.end_hour AS `Free time Start`,
  IFNULL(la.start_hour,a.end_hour) AS `Free Time End`,
  IFNULL(TIMEDIFF(la.start_hour, a.end_hour),'00:00:00') AS `Total Free Time`
FROM appointment AS a
  LEFT JOIN (SELECT * FROM appointment LIMIT 1,18446744073709551615) AS la
    ON la.id = (SELECT MIN(id) FROM appointment where id > a.id LIMIT 1)      

And the result is

+--------------------------------------------------------+
¦ id ¦ Free time Start ¦ Free Time End | Total Free Time |
¦----+-----------------¦---------------------------------|
¦  1 ¦   08:15:00      ¦ 14:00:00      |    05:45:00     |
¦  2 ¦   14:30:00      ¦ 17:00:00      |    02:30:00     |
¦  3 ¦   17:45:00      ¦ 21:00:00      |    03:15:00     |
¦  4 ¦   21:00:00      ¦ 21:00:00      |    00:00:00     |
+----------------------+---------------------------------+  

The points to learn from this query are

1. Timediff function usage. timediff('end time','start time')
2. Joining with upper number
3. Avoid first record in join with a long offset and limit starting from 1 instead of zero
4. IFNULL usage ifnull('if here comes null','select this then')

Answer 2

Try this Query i hope its work for you.....

SELECT
  a.id,
  a.end_hour    AS `Free time Start`,
  la.start_hour AS `Free Time End`,
  IFNULL(TIMEDIFF(la.start_hour, a.end_hour),'00:00:00') AS `Total Free Time`
FROM appointment AS a
  LEFT JOIN (SELECT *
             FROM appointment
             LIMIT 1,18446744073709551615) AS la
    ON la.id = (SELECT
                  id
                FROM appointment
                WHERE id NOT IN(a.id)
                ORDER BY (a.id > id)ASC
                LIMIT 1);

Answer 3

This will give you the end time blocks

SELECT T_a.end_hour
FROM (table AS T_a) LEFT JOIN (table AS T_b)
ON (T_a.`date`=T_b.`date` AND T_b.start_hour<=T_a.end_hour AND T_b.end_hour>T_a.end_hour)
WHERE T_b.user_id IS NULL

This will give you the start time block

SELECT T_a.start_hour
FROM (table AS T_a) LEFT JOIN (table AS T_b)
ON (T_a.`date`=T_b.`date` AND T_b.start_hour<T_a.start_hour AND T_b.end_hour>=T_a.start_hour)
WHERE T_b.user_id IS NULL

These queries will look for starts or ends that are uncrossed or butted up to other slots. so 10-11 11-12 will give 10 start, 12 end = free time is 08-10 and 12-21

So free time is 08:00 (unless its a start time) upto first 'start' time, then matching pairs of END->START upto last END->21:00 (unless 21:00 IS the last end)

N.B. You'll need to add the date in too.

Answer 4

Perhaps this is over kill but this works on sql-server, not sure the effort to convert to mysql

declare @AvailableTime table ( AvailableDate date,  StartTime time, EndTime time )

insert into @AvailableTime values 
('15 dec 2010', '08:00:00', '21:00:00')

declare @Booking table (BookingDate date, UserId int, StartTime Time, EndTime Time)

insert into @Booking values 
('15 dec 2010', 20, '08:00:00', '08:15:00'),
('15 dec 2010', 20, '14:00:00', '14:30:00'),
('15 dec 2010', 20, '17:00:00', '17:45:00')

select 
    *
from
(
    -- first SELECT get start boundry
    select t.StartTime s, b.StartTime e
    from @AvailableTime t, @Booking b
    where 
        t.AvailableDate = b.BookingDate and (t.StartTime <= b.EndTime and b.StartTime <= t.EndTime) and t.StartTime <> b.StartTime
    and
        not exists (select 1 from @Booking b2 where b2.BookingDate = b.BookingDate and b2.StartTime < b.StartTime)

    union

    -- second SELECT get spikes ie middle
    select b1.EndTime s, b2.StartTime e
    from @AvailableTime t, @Booking b1, @Booking b2
    where 
        t.AvailableDate = b1.BookingDate and (t.StartTime <= b1.EndTime and b1.StartTime <= t.EndTime) 
    and 
        t.AvailableDate = b2.BookingDate and (t.StartTime <= b2.EndTime and b2.StartTime <= t.EndTime) 
    and 
        b1.EndTime < b2.StartTime
    and
        not exists (select 1 from @Booking b3 where b3.BookingDate = t.AvailableDate and b3.StartTime > b1.EndTime and b3.EndTime < b2.StartTime)

    union

    -- third SELECT get end boundry
    select b.EndTime s, t.EndTime e
    from @AvailableTime t, @Booking b
    where 
        t.AvailableDate = b.BookingDate and (t.StartTime <= b.EndTime and b.StartTime <= t.EndTime) and t.EndTime <> b.EndTime
    and 
        not exists (select 1 from @Booking b2 where b2.BookingDate = b.BookingDate and b2.StartTime > b.StartTime)
) t1