SQL Query 和 case 语句通过连接两个表来显示多个条目

Question

这是两个表的示例，我想创建一个视图作为最终结果。有两个表作为视图的输入，一个具有具有位置 ID 的国家，另一个具有位置名称，我想加入它们，然后做一个案例以用单个条目替换多个计数。 任何帮助表示赞赏。

Here is the screenshot of how tables look like, Table Entity and Table Location as input tables to the view

我首先想到从实体表中获取多个位置 ID 的计数，然后创建一个 select Case 语句但没有用，这里是草稿代码。

select
    Country, count(locationid),
    case LocationName
        when Cnt > 1 then 'Mulitple offices'
        when Cnt = 0 then 'Unknown Location'
        else LocationName
    end
from 
    Entity 
group by 
    Country

更新： 我刚刚制作了一个SQLFiddle（非常方便）并实现了@Gordon 和@P.Eh 的两种解决方案，但存在一些问题。具体见下面的cmets

Answer 1

我认为这就是你想要的：
- 当 location 表中的 location_id 为 NULL 或 0 时，'Unknow location'

select
    COU.Country,
    case 
        when COU.pleace is null OR COU.pleace=0 then 'Unknow location'
        when COU.number_of_pleaces > 1 then 'Multiple offices'
        else coalesce(LOC.Location_name,'cound not math location')
    end as [location name]
from
    (   select country,
            sum(1) as number_of_pleaces,
            max(Location_id) as pleace
        from @entity
        group by country
    ) COU
    left join
    @location LOC
        on LOC.Location_id = COU.pleace
        and COU.number_of_pleaces = 1

Answer 2

你似乎想要这样的东西：

select e.Country, count(l.locationId),
       (case when count(l.locationId) > 1 Then 'Mulitple offices'
             when count(l.locationId) = 0  then 'Unknown Location'
             else max(l.LocationName)
        end)
from Entity e left join
     Location l
     on e.locationId = l.locationId
group by e.Country;