如何按月分组，如果某个月没有值，则返回零？

也许这不是最好的方法，但是它将解决您的问题。快速介绍：

SELECt 'January' AS mName, 1 AS mOrder, COALESCE(SUM(amount),0) AS total_num FROM income iWHERe month(i.date) = 1UNIOnSELECt 'February' AS mName, 2 AS mOrder, COALESCE(SUM(amount),0) AS total_num FROM income iWHERe month(i.date) = 2UNIOn...and go on