如何按月份分组，如果某个月份没有值，则返回零？

SELECT 
    DATE_FORMAT(date_column, '%Y-%m') AS month,
    COALESCE(SUM(value_column), 0) AS total_value
FROM 
    (
        SELECT 
            DATE_FORMAT(date_column, '%Y-%m') AS month,
            value_column
        FROM 
            table_name
        UNION ALL
        SELECT 
            DISTINCT DATE_FORMAT(date_column, '%Y-%m') AS month,
            0 AS value_column
        FROM 
            table_name
    ) AS subquery
GROUP BY 
    month
ORDER BY 
    month;