Find users with common dates in the respective date range

Question

I am trying to find a simple logic to get users who have common dates in the date range while they were active.
Example:
User A -   Effective start - 1/1/2015  and  Effective End = 1/9/2015
User B -  Effective start - 1/5/2015  and  Effective End = 1/30/2015
User C - Effective start - 3/1/2015  and  Effective End = 4/9/2015
So for the above scenario my SQL code should capture UserA and UserB , as they have common active dates between them.

Answer 1

DECLARE @YourTable TABLE
UserName varchar(128),
EffectiveStart date,
EffectiveEnd date
INSERT INTO @YourTable VALUES
('User A', '1/1/2015', '1/9/2015'), ('User B', '1/5/2015', '1/30/2015'), ('User C', '3/1/2015', '4/9/2015')
SELECT *
FROM @YourTable AS t1, @YourTable AS t2
WHERE t1.UserName <> t2.UserName
AND (
t1.EffectiveStart BETWEEN t2.EffectiveStart AND t2.EffectiveEnd
OR t1.EffectiveEnd BETWEEN t2.EffectiveStart AND t2.EffectiveEnd
OR t2.EffectiveStart BETWEEN t1.EffectiveStart AND t1.EffectiveEnd
OR t2.EffectiveEnd BETWEEN t1.EffectiveStart AND t1.EffectiveEnd
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