Longest/Shortest Distance [NCTU Floor 26]

/*Format : LIMIT a - 1, b - (a - 1)
  ROUND(lat/lon, n)
  ORDER BY city DESC(ra) OR ASC(al)
*/
SELECT ROUND(MAX(SQRT(POW(x1 - x2, 2) + POW(y1 - y2, 2))), 4),
       ROUND(MIN(SQRT(POW(x1 - x2, 2) + POW(y1 - y2, 2))), 4)
    FROM ((SELECT id, ROUND(lat, 3) x1, ROUND(lon, 3) y1
            FROM citytable GROUP BY x1, y1 ORDER BY city DESC, id LIMIT 5, 9) AS tt1
                JOIN
         (SELECT id, ROUND(lat, 3) x2, ROUND(lon, 3) y2
            FROM citytable GROUP BY x2, y2 ORDER BY city DESC, id LIMIT 5, 9) AS tt2
                ON tt1.id<>tt2.id AND tt1.id<tt2.id);