I have a MySQL table with the following fields:
This is a query pattern for which I found the answer many years ago:
SELECT * FROM mytable a JOIN 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_overlap before insert on mytable for each row begin 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;