How to calculate Median using MySQL

SET @ROW_NUMBER:=0; 
select round(avg(LAT_N),4) from 
(
select 
@Row_Number := @Row_Number +1 as count_of_group, 
LAT_N ,

(SELECT 
            COUNT(*)
        FROM
            Station 
        ) AS total_of_group

from station

 
order by Lat_N asc
    ) 
    tmp 
    where count_of_group
    between total_of_group / 2.0 AND total_of_group / 2.0 + 1