SQL条件加减法答案

【问题标题】：SQL conditional addition or subtractionSQL条件加减法
【发布时间】：2009-09-15 21:40:11
【问题描述】：

我有一张表，我需要在其中对某个字段进行一些简单的数学运算。我在 SQL 中尝试了嵌套的 SELECTS、IF/THEN 或 CASE 语句，但无济于事。

示例表：
wYear, yMonth, Account, Usage, Serv_code
2008, 9, 12345, 1000, 香蕉
2008, 9, 12345, 5000, 香蕉
2008, 9, 12345, 4000, 苹果
2007, 5, 54321, 1500, 香蕉

我需要按 wYear、yMonth、Account 分组并添加“Usage” WHERE Serv_code = 'Banana'...

选择 wYear、yMonth、Account、SUM(Usage) 作为“Totals”
来自我的表
WHERE Serv_code = '香蕉'
GROUP BY wYear, yMonth, Account

但是我碰壁的地方是 - 如果“Serv_code”确实等于“Apple”（WHERE Serv_code = 'Apple'），我需要从 SUM（Usage）中减去“Apple”Usage。

使用上表的示例结果：
2008, 9, 12345, 2000
2007, 5, 54321, 1500

当谈到 SQL 时，我是个 hack，答案很简单，但那是其中之一。

【问题讨论】：

如果您包含用于测试数据的 create table 和 insert 语句，则回答此类问题会更容易。

标签： sql

【解决方案1】：

您可以根据 Serv_code 中的值使用 case 语句获取正值或负值：

select wYear, yMonth, Account, sum(Usage * case Serv_code when 'Apple' then -1 else 1 end) as "Totals"
from myTable
where Serv_code in ('Banana', 'Apple')
group by wYear, yMonth, Account

【讨论】：

【解决方案2】：

我希望这是你想要的：

SELECT 
    banana.wYear, 
    banana.yMonth, 
    banana.Account, 
    totals_banana - totals_apple AS totals
FROM
(
    SELECT wYear, yMonth, Account, SUM(Usage) as "totals_banana"
    FROM myTable 
    WHERE Serv_code = 'Banana'
    GROUP BY wYear, yMonth, Account
) banana
INNER JOIN 
(
    SELECT wYear, yMonth, Account, SUM(Usage) as "totals_apple"
    FROM myTable 
    WHERE Serv_code = 'Apple'
    GROUP BY wYear, yMonth, Account
) apple 
ON 
     banana.wYear = apple.wYear 
     AND banana.yMonth = apple.yMonth 
     AND banana.Account = apple.Account

【讨论】：

【解决方案3】：

SELECT wYear, yMonth, Account, SUM(case when Serv_code  = 'Banana' then
Usage when Serv_Code = 'Apple' then -Usage else 0 end) as "Totals"
FROM myTable

GROUP BY wYear, yMonth, Account

测试友好版本

Declare @myTable table (wYear int, ymonth int, Account varchar(20), 
Usage int, Serv_Code varchar(20))

Insert into @mytable values (2008, 9, '12345', 1000, 'Banana')
Insert into @mytable values (2008, 9, '12345', 5000, 'Banana')
Insert into @mytable values (2008, 9, '12345', 4000, 'Apple')
Insert into @mytable values (2007, 5, '54321', 1500, 'Banana')

SELECT wYear, yMonth, Account, SUM(case when Serv_code  = 'Banana' then
Usage when Serv_Code = 'Apple' then -Usage else 0 end) as "Totals"
FROM @myTable

GROUP BY wYear, yMonth, Account


wYear   yMonth  Account Totals
2007    5   54321   1500
2008    9   12345   2000

【讨论】：

【解决方案4】：

我怀疑它的效率，但这应该可以解决问题

SELECT 
    wYear, yMonth, Account, 
    (
      (SELECT SUM(Usage) FROM myTable AS m 
        WHERE m.wYear=wYear AND 
              m.yMonth=yMonth AND 
              m.Account=Account AND 
              m.Serv_code='Banana') -
      (SELECT SUM(Usage) FROM myTable AS m 
        WHERE m.wYear=wYear AND 
              m.yMonth=yMonth AND 
              m.Account=Account AND 
              m.Serv_code='Apple')
   ) as "Totals"
FROM myTable 
GROUP BY wYear, yMonth, Account

【讨论】：

【解决方案5】：

也许这可行 -

选择 wYear、yMonth、Account、 SUM（当 Usage = 'Apple' then usage*-1 else Usage end）为“Totals” 从我的表 WHERE Serv_code = '香蕉' GROUP BY wYear, yMonth, Account

【讨论】：