mysql 分组内中位数

SELECT 
    group_column, 
    AVG(value_column) AS median
FROM (
    SELECT 
        group_column, 
        value_column, 
        @rownum := @rownum + 1 AS row_number,
        @total_rows := COUNT(*) OVER (PARTITION BY group_column) AS total_rows
    FROM 
        your_table, 
        (SELECT @rownum := 0) r
    ORDER BY 
        group_column, 
        value_column
) AS subquery
WHERE 
    row_number IN (FLOOR((@total_rows + 1) / 2), FLOOR((@total_rows + 2) / 2))
GROUP BY 
    group_column;

SELECT 
    region, 
    AVG(amount) AS median
FROM (
    SELECT 
        region, 
        amount, 
        @rownum := @rownum + 1 AS row_number,
        @total_rows := COUNT(*) OVER (PARTITION BY region) AS total_rows
    FROM 
        sales, 
        (SELECT @rownum := 0) r
    ORDER BY 
        region, 
        amount
) AS subquery
WHERE 
    row_number IN (FLOOR((@total_rows + 1) / 2), FLOOR((@total_rows + 2) / 2))
GROUP BY 
    region;