兩個不相關或有主鍵的表上的 SQL 連接

Question

我有以下查詢：-

select
dbo.table1.service,
dbo.table1.level_3_structure,
Sum(table1.Reduced) as Total_Reduced

from dbo.table1

where 
dbo.table1.Period = 'Cumulative'

Group by 
dbo.table1.service,
dbo.table1.level_3_structure

結果與此類似：-

service          level_3_structure   Total_Reduced
Service 1            Structure1          11.76
Service 2            Structure2         239.86
Service 3            Structure3         940.29

我有另一個表（表 2），其中包含值 service 和 level_3_structure，還包含一個名為“FTE”的列。

我想要做的是根據服務和 level_3_structure 加入這個表並返回 FTE 的總和。

我已經嘗試了下面的查詢，但它似乎為每個加工行復制了 table1，從而產生了大約 830 萬個結果。

select
dbo.table1.service,
dbo.table1.level_3_structure,
Sum(dbo.table1.Reduced) as Total_Reduced,
Sum(dbo.table2.fte) as 'Total FTE'

from dbo.table1
left join dbo.table2
on dbo.table1.service = dbo.table2.service and
   dbo.table1.level_3_structure = dbo.table2.level_3_structure

where 
dbo.table1.Period = 'Cumulative'

Group by 
dbo.table1.service,
dbo.table1.level_3_structure

Answer 1

如果您的第一個查詢返回您需要的行，那么您可以將它（而不是 table1）加入到 table2：

select service, level_3_structure, Total_Reduced, sum(fte) as Total_FTE
from (
    select 
    dbo.table1.service, 
    dbo.table1.level_3_structure, 
    Sum(table1.Reduced) as Total_Reduced 

    from dbo.table1 

    where  
    dbo.table1.Period = 'Cumulative' 

    Group by  
    dbo.table1.service, 
    dbo.table1.level_3_structure 
) t1
inner join table2 on t1.service = table2.service 
AND t1.level_3_structure = table2.level_3_structure 

    Group by  
    dbo.table1.service, 
    dbo.table1.level_3_structure 

不過，聽起來您的 table1 應該有列 fte。