mysql_quantile.sql

SELECT AVG(t1.`value`) AS median_val FROM (
SELECT @rownum:=@rownum+1 AS `row_number`, d.`value`
  FROM `data` d,  (SELECT @rownum:=0) r
  WHERE 1 -- use self where
  ORDER BY d.`value`
) AS t1, 
(
  SELECT count(*) AS total_rows
  FROM `data` d
  WHERE 1 -- use self where
) AS t2
WHERE 1
-- 0.5 - median
AND t1.row_number IN ( floor((total_rows+1) * 0.5), floor((total_rows+2) * 0.5) );