使用case语句设置值

Question

表\n：

Rate

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

Amount

任何帮助都可以，我正在努力编写将使用表1中的不同费率更新表的案例陈述。

我试过了：

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

我希望应用的费率为费率A1，区域为inter / Intra，具体取决于Amount表中的Region

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

我想要应用的费率是费率A2和地区是inter / Intra，具体取决于Amount表中的Region） 等

请帮忙

Answer 1

这是一种方法

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

我知道你的表格是如何相关的。

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')

使用子查询的一个优点是，如果返回多行，则会出现错误。有理由避免使用update ... from ...语法。根据示例数据，您似乎将拥有空值，因此如果您选择以此方式执行此操作，则需要使用outer join而不是inner join。