在MySQL中运行多个类别的总和

Question

我有一张表格

 Category      Time      Qty  
     A           1        20 
     B           2         3
     A           3        43
     A           4        20
     B           5        25

我需要在MySQL中按类别计算运行总计.结果看起来像这样:

 Category      Time      Qty     Cat.Total  
     A           1        20         20
     B           2         3          3
     A           3        43         63
     A           4        20         83
     B           5        25         28

知道如何在MySQL中有效地做到这一点吗？我搜索的范围很广,但我能找到的是有关如何在MySQL中插入一个单独运行总计的信息.我想知道是否有任何方法可以使用GROUP BY或类似的构造来实现这一目标.

Answer 1

您可以在子查询中计算总和:

select  Category
,       Time
,       Qty
,       (
        select  sum(Qty) 
        from    YourTable t2 
        where   t1.Category = t2.Category 
                and t1.Time >= t2.Time
        ) as CatTotal
from    YourTable t1

交易可读性的速度,您可以使用MySQL变量来保持运行总和:

select  Category
,       Time
,       Qty
,       @sum := if(@cat = Category,@sum,0) + Qty as CatTotal
,       @cat := Category
from    YourTable
cross join
        (select @cat := '', @sum := 0) as InitVarsAlias
order by
        Category
,       Time

此构造需要排序才能工作; 如果需要不同的顺序,请将查询包装在子查询中:

select  Category
,       Time
,       Qty
,       CatTotal
from    (
        select  Category
        ,       Time
        ,       Qty
        ,       @sum := if(@cat = Category,@sum,0) + Qty as CatTotal
        ,       @cat := Category
        from    YourTable
        cross join
                (select @cat := '', @sum := 0) as InitVarsAlias
        order by
                Category
        ,       Time
        ) as SubQueryAlias
order by
        Time