MySQL:计算中值

Question

我正在尝试计算价格的中位数。我在这里找到了如何做的答案- Simple way to calculate median with MySQL ，但这对我不起作用，我得到的结果是空的。谁能帮忙？

SELECT x.price from mediana as x, mediana y
GROUP BY x.price
HAVING SUM(SIGN(1-SIGN(y.price-x.price))) = (COUNT(*)+1)/2

Answer 1

AFAIU 你的问题。

This answer @velcrow 成功计算中值。不幸的是，当行数为偶数而不是计算中间 2 行的平均值时，查询只返回第二个值。我已对查询进行了一些修改以满足您的需要:

--average value for middle rows
SELECT avg(t1.price) as median_val FROM (
SELECT @rownum:=@rownum+1 as `row_number`, d.price
  FROM mediana d,  (SELECT @rownum:=0) r
  WHERE 1
  -- put some where clause here
  ORDER BY d.price
) as t1, 
(
  SELECT count(*) as total_rows
  FROM mediana d
  WHERE 1
  -- put same where clause here
) as t2
WHERE 1
--this condition should return one record for odd number of rows and 2 middle records for even.
AND t1.row_number>=total_rows/2 and t1.row_number<=total_rows/2+1; 

Test on sample data on sqlfiddle