Thanks tye and fenLisesi. I initially started with a database model but found it to be more cumbersome. After your good advice, I created a view and ran fenLisesi query with some modifications. It did the trick. Its slow though but it gets me what I need. I'll benchmark it with Perl code to see which is more efficient. You monks rock!!!

create view foo as select session_id, start_session, end_session, user
+_id from bar;
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</code> Then I ran

SELECT DISTINCT foo.user_id AS user, 
foo.session_id  AS session1,
bar.session_id  AS session2,
foo.start_session AS start1,
bar_.start_session AS start2,
foo.end_session AS end1,
bar_.end_session AS end2 FROM foo,bar

WHERE foo.user_id != bar_.user_id 
AND bar_.start_session >= foo.start_session 
AND bar_.start_session <= foo.end_session 
AND foo.session_id != bar_.session_id 
order by start1 ASC;
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