SQL generate free slots on the fly from bookings table? - mysql

Question

I know there's a lot of booking questions on php section.
Belive me when i tell you that I tried most of them, at least those which seems compatible. So let me explain.
I have this appointments table
ID | day | start | end |
----------------------------------
1 | 01-01-2018 | 09:00 | 10:00 |
2 | 01-01-2018 | 10:00 | 13:00 |
3 | 02-01-2018 | 12:00 | 15:00 |
4 | 02-01-2018 | 18:00 | 19:30 |
I was wondering, it possibile with sql to get empty time slots? The result should like something like:
day | start | end
---------------------------
01-01-2018 | 00:00 | 09:00
01-01-2018 | 13:00 | 23:59
02-01-2018 | 00:00 | 12:00
02-01-2018 | 15:00 | 18:00
02-01-2018 | 19:30 | 23:59
The query should contain 2 dates: start_day + end_day
I prepared a fiddle here: https://www.db-fiddle.com/f/6dm8q8UtmDkkkjExYfMEbx/1

Answer 1

MSSQL Version
WITH X AS
(
SELECT ROW_NUMBER() OVER (ORDER BY Day, Start)sq, [Day], [Start], [End]
FROM (
SELECT [Day], [Start], [End]
FROM [appointments]
UNION
SELECT Day, '00:00', '00:00'
FROM [appointments]
UNION
SELECT Day, '23:59', '23:59'
FROM [appointments]
) T1
)
SELECT A.Day, A.[End] AS Start, b.[Start] AS End
FROM x A
JOIN x B
ON A.sq = B.sq -1
AND A.[Day] = B.[Day]
AND A.[End] <> b.[Start]
Mysql 5.7 version
SET #RowNumber = 0;
CREATE TABLE cte
SELECT (#RowNumber := #RowNumber+1) AS Rownumber, Day, Start, End
FROM (
SELECT Day, Start, End
FROM booking
UNION
SELECT Day, '00:00', '00:00'
FROM booking
UNION
SELECT Day, '23:59', '23:59'
FROM booking
) T1
ORDER BY day ASC, Start ASC
;
SELECT A.Day, A.End AS Start, B.Start AS End
FROM cte A
JOIN cte B
ON A.Rownumber = B.Rownumber -1
AND A.Day = B.Day
AND A.End <> B.Start
ORDER BY A.Day asc, A.End asc
Will add a fiddle to demonstrate
https://www.db-fiddle.com/f/6dm8q8UtmDkkkjExYfMEbx/2
Mysql 5.7 including days without bookings
SET #RowNumber = 0;
CREATE TABLE cte
SELECT (#RowNumber := #RowNumber+1) AS Rownumber, Day, Start, End
FROM (
SELECT Day, Start, End
FROM booking
UNION
SELECT Day, '00:00', '00:00'
FROM booking
UNION
SELECT Day, '23:59', '23:59'
FROM booking
) T1
ORDER BY day ASC, Start ASC
;
SELECT DAY, Start, End
FROM(
SELECT A.Day, A.End AS Start, B.Start AS End
FROM cte A
JOIN cte B
ON A.Rownumber = B.Rownumber -1
AND A.Day = B.Day
AND A.End <> B.Start
UNION
SELECT DATE_ADD(A.Day, INTERVAL 1 DAY) AS Day, B.Start AS Start, A.End AS End
FROM cte A
JOIN cte B
ON A.Rownumber = B.Rownumber -1
AND A.Day <> B.Day
)Result
ORDER BY Day ASC, Start ASC
https://www.db-fiddle.com/f/6dm8q8UtmDkkkjExYfMEbx/3

Answer 2

Here is a solution below. Assumed the logic of ID column is identity(1,1), otherwise please generate row_number() for each column first. Syntax might not match with MySql, but you will get the logic and apply same if u like.
CREATE TABLE #result (
[day] date NOT NULL,
[start] time NOT NULL,
[end] time NOT NULL
)
declare #maxid int = (select max(id) from #booking), #counter int = 1, #day date
declare #tempStart time = '00:00', #currentStart time ='00:00'
declare #tempDay date = (select TOP 1 [day] from #booking)
while #counter <= #maxid
begin
set #currentStart = (select start from #booking where id=#counter)
set #day = (select [day] from #booking where id=#counter)
if (#day > DATEADD(day,1,#tempDay))
begin
insert into #result values (DATEADD(day,1,#tempDay),'00:00', '23:00')
set #tempDay = #day
end
if(#tempStart < #currentStart)
begin
insert into #result values (#day, #tempStart, #currentStart)
end
if(#counter = #maxid and #tempStart <> '23:59')
begin
insert into #result values (#day, (select [end] from #booking where id=#counter), '23:59')
end
set #tempStart = (select [end] from #booking where id=#counter)
set #counter = #counter + 1
end
select * from #result
Example for SQL Server: https://rextester.com/live/VBNJ34000