mysql查询中位数

mysql无直接查询中位数的函数median,实现方式有多种

SELECt AVG(dd.val) as median_val
FROM (
SELECt d.val, @rownum:=@rownum+1 as `row_number`, @total_rows:=@rownum
  FROM data d, (SELECT @rownum:=0) r
  WHERe d.val is NOT NULL
  -- put some where clause here
  ORDER BY d.val
) as dd
WHERe dd.row_number IN ( FLOOR((@total_rows+1)/2), FLOOR((@total_rows+2)/2) );