Detect overlapping date ranges from the same table

Question

I have a table with the following data

PKey  Start       End         Type
====  =====       ===         ====
01    01/01/2010  14/01/2010  S
02    15/01/2010         


        

Answer 1

In MySQL you basically need:

SELECT COUNT(*) FROM date_ranges AS A, date_ranges AS B WHERE A.id <> B.id AND A.id > B.id AND A.end_at > B.start_at AND B.end_at > A.start_at

> in the second and the third statement can be replaced with >= to follow includes matching.

This topic is related to the "Allen's Interval Algebra" and there are some more reading on this can be found by those links:

• http://www.ics.uci.edu/~alspaugh/cls/shr/allen.html
• http://salman-w.blogspot.com.es/2012/06/sql-query-overlapping-date-ranges.html