MySQL：計數中位數值

Question

我正在計算價格的中位數。 我創建了答案如何在這裏做到這一點，Simple way to calculate median with MySQL，但它不適合我，我得到空的結果。 任何人都可以幫忙嗎？

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你的問題。

This answer by @velcrow成功地計算了中值。不幸的是，當有偶數行而不是計算2箇中間行的查詢的平均值時，只返回第二個值。我做了一對夫婦對查詢的修改，以適應您的需求：

--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