Detect if two timings clash / intersect or not

I am currently developing an event management system where the database stores time slots as such:

SlotId | DateTime            | Duration  
-------+---------------------+---------------
 1     | 2011-06-06 15:00:00 | 5.0
 2     | 2011-06-06 14:00:00 | 3.0
 3     | 2011-06-07 11:00:00 | 8.0

Note that Duration is a DOUBLE in hours and DateTime is a TIMESTAMP.

In the table, we can clearly see that time slots 1 and 2 clashes, 开发者_Python百科whereas time slots 2 & 3 and time slots 1 & 3 doesn't clash. How can we write the SQL statement to detect clashes between the two time slots?

Maybe I'm confused, but it looks like all three of those time slots overlap. Since they go From 11:00 - 19:00, 14:00 - 17:00, and 15:00 - 20:00 respectively (in reverse of your order, chronologically by start time). But if I understand your table correctly here is the code to find the overlaps

SELECT CONCAT(T1.SlotId,  ' Overlaps ', T2.SlotId)
FROM YourTable AS T1 JOIN YourTable AS T2 
WHERE T1.SlotId <> T2.SlotId AND 
    T1.DateTime <= T2.DateTime AND 
    DATE_ADD(T1.DateTime,INTERVAL SEC_TO_TIME(T1.Duration * 3600) HOUR_SECOND) > T2.DateTime