Checking a table for time overlap?

This is a query pattern for which I found the answer many years ago:

SELECT *FROM mytable aJOIN mytable b on a.starttime <= b.endtime    and a.endtime >= b.starttime    and a.name != b.name; -- ideally, this would compare a "key" column, eg id

To find "any overlap", you compare the opposite ends of the timeframe with each other. It's something I had to get a pen and paper out for and draw adjacent ranges to realise that the edge cases boiled down to this comparison.

If you want to prevent any rows from overlapping, put a variant of this query in a trigger:

create trigger mytable_no_overlapbefore insert on mytablefor each rowbegin  if exists (select * from mytable             where starttime <= new.endtime             and endtime >= new.starttime) then    signal sqlstate '45000' SET MESSAGE_TEXT = 'Overlaps with existing data';  end if;end;

I wanted a generic function to check if two time ranges for days overlap which would also work with cases where the schedule starts before midnight and ends after, like "17:00:00-03:00:00" and "14:00:00-01:00:00" should overlap, so I modified the solution by Bohemian

you use this function as follows

SELECT func_time_overlap("17:00:00","03:00:00", "14:00:00","01:00:00")

or in your case like this

SELECT *FROM mytable aJOIN mytable b ON (    a.name != b.name     AND func_time_overlap(a.starttime, a.endtime, b.starttime, b.endtime));

Here is the function definition

CREATE FUNCTION `func_time_overlap`(a_start TIME, a_end TIME, b_start TIME, b_end TIME) RETURNS tinyint(1) DETERMINISTICBEGIN-- there are only two cases when they don't overlap, but a lot of possible cases where they do overlap-- There are two time formats, one is an interval of time that can go over 24 hours, the other is a daily time format that never goes above 24 hours-- by default mysql uses TIME as an interval-- this converts a TIME interval into a date time format-- I'm not using `TIME(CAST(a_start AS DATETIME));` to convert the time interval to a time-- because it uses the current day by default and might get affected by the timezone settings of the database, -- just imagine the next day having the DST change.-- although the CAST should work fine if you use UTCIF a_start >= 24 THEN     SET a_start = TIME(CONCAT(MOD(HOUR(a_start), 24),':',MINUTE(a_start),':',SECOND(a_start))); END IF;IF b_start >= 24 THEN     SET b_start = TIME(CONCAT(MOD(HOUR(b_start), 24),':',MINUTE(b_start),':',SECOND(b_start))); END IF;IF a_end > 24 THEN     SET a_end = TIME(CONCAT(MOD(HOUR(a_end), 24),':',MINUTE(a_end),':',SECOND(a_end))); END IF;IF b_end > 24 THEN     SET b_end = TIME(CONCAT(MOD(HOUR(b_end), 24),':',MINUTE(b_end),':',SECOND(b_end))); END IF;-- if the time range passes the midnight mark, then add 24 hours to the timeIF a_start >= a_end THEN     SET a_end = a_end + INTERVAL 24 HOUR; END IF;IF b_start >= b_end THEN     SET b_end = b_end + INTERVAL 24 HOUR; END IF;RETURN a_start < b_end AND a_end > b_start;END

I'm not using TIME(CAST(a_start AS DATETIME)); to convert the time interval to a time because it uses the current day by default and might get affected by the timezone settings of the database, just imagine the next day having the DST change.

If your database is using UTC timezone (as it should) then you can use this

IF a_start >= 24 THEN     SET a_start = TIME(CAST(a_start AS DATETIME)); END IF;IF b_start >= 24 THEN     SET b_start = TIME(CAST(b_start AS DATETIME)); END IF;IF a_end > 24 THEN     SET a_end = TIME(CAST(a_end AS DATETIME));END IF;IF b_end > 24 THEN     SET b_end = TIME(CAST(b_end AS DATETIME));END IF;

Try this:

declare @tempTbl table(RecID)    insert into @tempTbl    Select RecID    from     (    Select t.RecID from Table1 t,Table1 t1    where t.StartTime between t1.StartTime AND t1.EndTime    AND t.RecID <> t1.RecID      )