You could use SQL, as tye hinted. Suppose you load your data into a table named sesn (session) with fields sesn_id, usr_id, sesn_bgn, sesn_end and whatever else you may need, properly indexed etc. Then, a query like the following should do what you want (untested): 
SELECT
    foo.usr_id   AS user,
    foo.sesn_id  AS session1,
    bar.sesn_id  AS session2,
    foo.sesn_bgn AS start1,
    bar.sesn_bgn AS start2,
    foo.sesn_end AS end1,
    bar.sesn_end AS end2
FROM
    sesn foo,
    sesn bar
WHERE
    foo.usr_id = bar.usr_id
    AND bar.sesn_bgn >= foo.sesn_bgn
    AND bar.sesn_bgn <= foo.sesn_end
    AND foo.sesn_id != bar.sesn_id
    -- AND (conditions on min duration etc here)

[download]

Here I have assumed that you are trying to track multiple simultaneous sessions by the same user. If that's not what you meant, adjust accordingly.

Hope this helps. Cheers.

In reply to Re: How to Iterate to Identify Concurrent Users (SQL) by fenLisesi
in thread How to Iterate to Identify Concurrent Users by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.