使用case語句設置值

Question

表Rate ：

Fees | Region  | Rate
-----+---------+---------
 A1  | Intra   | 0.00015   
 A2  | Intra   | 0.000325   
 A3  | Inter   | 0.000025   
 A4  | Inter   | 0.015  

表Amount ：

Region | Amount | A1 | A2 | A3 | A4
-------+--------+----+----+----+----
Intra  | $10    |  ? |  ? |  ? |  ?
Intra  | $11    |  ? |  ? |  ? |  ?
Inter  | $12    |  ? |  ? |  ? |  ?
Inter  | $13    |  ? |  ? |  ? |  ?

任何幫助都可以，我正在努力編寫case語句，以使用表1中的不同比率更新表。

我努力了：

Update a
set A.A1 = Amount * R.Rate
from dbo.Amount as A 
inner join dbo.Rate R where R.Region = A.region

我希望應用的比率是比率A1，區域是內部/內部，具體取決於金額表中的區域

Update a
set A.A2 = Amount * R.Rate
from dbo.Amount as A 
inner join dbo.Rate R where R.Region = A.region

我希望應用的比率是比率A2，而區域是內部/內部，具體取決於金額表中的區域）等

請幫忙

Answer 1

這是一種方法

Update a
set 
A.A1 = Amount* R1.Rate
,A.A2 = Amount* R2.Rate
,A.A3 = Amount* R3.Rate
,A.A4 = Amount* R4.Rate
from dbo.Amount as A 
inner join dbo.Rate R1 
on R1.Region = A.region and r1.fees = 'A1'
inner join dbo.Rate R2 
on R2.Region = A.region and r2.fees = 'A2'
inner join dbo.Rate R3 
on R3.Region = A.region and r3.fees = 'A3'
inner join dbo.Rate R4 
on R4.Region = A.region and r4.fees = 'A4'

Answer 2

我收集到的是您的表之間的關系。

update Amount
set
    A1 = Amount * (select Rate from Rate where Region = Amount.Region and Fees = 'A1'),
    A2 = Amount * (select Rate from Rate where Region = Amount.Region and Fees = 'A2'),
    A3 = Amount * (select Rate from Rate where Region = Amount.Region and Fees = 'A3'),
    A4 = Amount * (select Rate from Rate where Region = Amount.Region and Fees = 'A4')

使用子查詢的優點之一是，如果返回多個行，則會出現錯誤。 有理由避免update ... from ...語法update ... from ... 。 根據示例數據，您似乎將具有null，因此，如果您選擇以這種方式使用，則將要使用outer join而不是inner join 。