MySQL median value - http://stackoverflow.com/a/7263925/313113

mysql_median_value.sql

SELECT round(avg(t1.LAT_N), 4) as median_val 
FROM (
    SELECT @rownum := @rownum+1 as `row_number`, 
           s.LAT_N
    FROM STATION s,
         (SELECT @rownum := 0) r
    ORDER BY s.LAT_N
) as t1, 
(
  SELECT count(*) as total_rows
  FROM STATION s
) as t2
WHERE t1.row_number in ( floor((total_rows+1)/2), floor((total_rows+2)/2) );