MySQL：计数中位数值

Question

我正在计算价格的中位数。 我创建了答案如何在这里做到这一点，Simple way to calculate median with MySQL，但它不适合我，我得到空的结果。 任何人都可以帮忙吗？

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 by @velcrow成功地计算了中值。不幸的是，当有偶数行而不是计算2个中间行的查询的平均值时，只返回第二个值。我做了一对夫妇对查询的修改，以适应您的需求：

--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