php - 如何在mysql中使用inner join或group by从两个表中获取所有余额值？

Question

我有两张 table

表名:年份

表名:月份

预期输出:

我对上面的输出使用下面的查询，但我得到了意想不到的结果。

SELECT a.id
     , SUM(a.no_of_units_purchase) 
  FROM month a
     , year b 
 WHERE a.id=b.id 
 GROUP 
    by b.id

上述查询的输出:

请指导我获得预期的结果..

提前致谢..

Answer 1

您应该使用左联接 而不是简单的联接，因为表格月份不能包含给定年份的购买。可行的查询是:

select year.id,
       year.no_of_units,
       sum(ifnull(month.no_of_units_purchase, 0)) as no_of_units_purchase,
       year.no_of_units - sum(ifnull(month.no_of_units_purchase, 0)) as balance_units
from   year
       left join month on year.id = month.id
group by
       year.id, 
       year.no_of_units