SELECT *
  FROM OrgChart Boss
 WHERE NOT EXISTS
       (SELECT *
          FROM OrgChart Workers
         WHERE Workers.lft > Boss.lft
           AND Workers.lft < Boss.rgt);

SELECT *
  FROM OrgChart Workers
 WHERE NOT EXISTS
       (SELECT *
          FROM OrgChart Boss
        WHERE Workers.lft > Boss.lft
          AND Workers.lft < Boss.rgt);

SELECT Children.emp , COUNT(Parents.emp) AS level
  FROM OrgChart Parents, OrgChart Children
 WHERE Children.lft BETWEEN Parents.lft AND Parents.rgt
GROUP BY Children.emp;

SELECT Boss.emp AS boss, Worker.emp AS worker
  FROM OrgChart Boss
       LEFT OUTER JOIN OrgChart Worker
       ON Boss.lft = (SELECT MAX(lft) ←左端座標が最大
                     FROM OrgChart
                    WHERE Worker.lft > lft
                      AND Worker.lft < rgt);

SELECT Worker.emp AS worker, Boss.emp AS boss
  FROM OrgChart Worker
       LEFT OUTER JOIN OrgChart Boss
         ON Boss.lft < Worker.lft
        AND Boss.lft = (SELECT MAX(lft)
                          FROM OrgChart
                         WHERE Worker.lft > lft
                          AND Worker.lft < rgt);