WEB LISTING 2: Query That Returns Session Groups'
Start and End Times

SELECT DISTINCT
  username,
  starttime,
  (SELECT MIN(endtime)
   FROM Sessions AS S3
   WHERE S3.username = S1.username
     AND S3.endtime >= S1.starttime
     AND ISNULL(
           (SELECT MIN(starttime)
            FROM Sessions AS S4
            WHERE S4.username = S1.username
              AND S4.endtime > S3.endtime),
           S3.endtime + 1) > S3.endtime)
  AS endtime
FROM Sessions AS S1
WHERE ISNULL(
        (SELECT MAX(endtime)
         FROM Sessions AS S2
         WHERE S2.username = S1.username
           AND S2.starttime < S1.starttime),
        S1.starttime -1) < S1.starttime