SQL GROUP BY 一列的不同值

Question

在我的 SQL Server 上，我得到了下表 - 简化了:

year    month    category    value
2009    9        1           10
2009    9        2           20
2009    9        3           40
...     ...      ...         ...

现在我想按年、月和类别 (1+2, 3, ...) 分组，以便我的结果如下所示:

year    month    category    value
2009    9        1+2         30
2009    9        3           40
...     ...      ...         ...

无法对表进行任何更改。此外，重要的是 SQL 运行速度快......

如何使这个 GROUP BY？我还没有找到任何有用的东西......

谢谢你的帮助...

Answer 1

with cte as (
   select
       year, month, value,
       case
           when category in (1, 2) then '1+2'
           else cast(category as varchar(max))
       end as category
   from Table1
)
select
    year, month, category, sum(value)
from cte
group by year, month, category

或者

select
    t.year, t.month, isnull(c.category, t.category), sum(value)
from Table1 as t
    left outer join (values
        (1, '1+2'),
        (2, '1+2')
    ) as c(id, category) on c.id = t.category
group by t.year, t.month, isnull(c.category, t.category)

sql fiddle demo