What is a simple and efficient way to find rows with time-interval overlaps in SQL?

Question

I have two tables, both with start time and end time fields. I need to find, for each row in the first table, all of the rows in the second table where the time intervals in

Answer 1

It's sound very complicated until you start working from reverse. Below I illustrated ONLY GOOD CASES (no overlaps)! defined by those 2 simple conditions, we have no overlap ranges if condA OR condB is TRUE, so we going to reverse those: NOT condA AND NOT CondB, in our case I just reversed signs (> became <=)

/*
|--------| A                             \___  CondA: b.ddStart >  a.ddEnd
            |=========| B                /      \____ CondB:  a.ddS >  b.ddE
                          |+++++++++| A         /
*/
--DROP TABLE ran
create table ran ( mem_nbr int, ID int, ddS date, ddE date)
insert ran values  
(100, 1,  '2012-1-1','2012-12-30'),    ----\ ovl
(100, 11, '2012-12-12','2012-12-24'),  ----/
(100, 2, '2012-12-31','2014-1-1'),
(100, 3, '2014-5-1','2014-12-14') ,

(220, 1, '2015-5-5','2015-12-14') ,    ---\ovl
(220, 22, '2014-4-1','2015-5-25') ,    ---/
(220, 3, '2016-6-1','2016-12-16')  

select  DISTINCT a.mem_nbr ,  a.* , '-' [ ], b.dds, b.dde, b.id 
FROM ran a
join ran b  on  a.mem_nbr = b.mem_nbr          -- match by mem#
               AND     a.ID <> b.ID            -- itself
                  AND     b.ddS <= a.ddE        -- NOT    b.ddS >  a.ddE       
                  AND     a.ddS <= b.ddE        -- NOT    a.ddS >  b.ddE