在一个 SQL SELECT 查询中向多个计数添加百分比答案

【问题标题】：Adding percentages to multiple counts in one SQL SELECT Query在一个 SQL SELECT 查询中向多个计数添加百分比
【发布时间】：2009-10-05 17:29:50
【问题描述】：

我有一个类似于下面的 SELECT 语句，它在一个查询中返回多个计数。

SELECT  invalidCount = (SELECT COUNT(*) FROM <...a...> WHERE <...b...>),
        unknownCount = (SELECT COUNT(*) FROM <...c...> WHERE <...d...>),
        totalCount   = (SELECT COUNT(*) FROM <...e...> WHERE <...f...>)

这很好用，但我想在 SELECT 中添加两个百分比列：

invalidCount * 100 / totalCount AS PercentageInvalid, 
unknownCount * 100 / totalCount AS UnknownPercentage

如何修改我的 SELECT 语句来处理这个问题？

【问题讨论】：

标签： sql sql-server sql-server-2005

【解决方案1】：

您可以在from 子句中使用子查询：

select
    s.invalidCount,
    s.unknownCount,
    s.totalCount,
    invalidCount * 100 / s.totalCount as PercentageInvalid,
    unknownCount * 100 / s.totalCount as PercentageUnknown
from
    (select  invalidCount = (SELECT COUNT(*) FROM <...a...> WHERE <...b...>),
        unknownCount = (SELECT COUNT(*) FROM <...c...> WHERE <...d...>),
        totalCount       = (SELECT COUNT(*) FROM <...e...> WHERE <...f...>)) s

【讨论】：

【解决方案2】：

SELECT invalidCount, 
  unknownCount, 
  totalCount, 
  invalidCount * 100 / totalCount AS PercentageInvalid, 
  unknownCount * 100 / totalCount AS UnknownPercentage 
FROM 
    (
      SELECT  invalidCount = (SELECT COUNT(*) FROM <...a...> WHERE <...b...>),  
      unknownCount = (SELECT COUNT(*) FROM <...c...> WHERE <...d...>),     
      totalCount       = (SELECT COUNT(*) FROM <...e...> WHERE <...f...>)
    )

【讨论】：

不要忘记 CAST(totalCount as float) - 否则你正在做整数除法......

【解决方案3】：

这是一种使用 OVER 子句的不同方法，非常酷 - 非常有效。看看这个针对 AdventureWorks 的示例：

SELECT DISTINCT CardType 
        ,COUNT(*) OVER (PARTITION BY CardType) AS TypeCount
        ,COUNT(*) OVER (PARTITION BY 1) AS TotalCount
        ,COUNT(*) OVER (PARTITION BY CardType) / CAST(COUNT(*) OVER (PARTITION BY 1) AS float) AS TypePercent
FROM Sales.CreditCard

【讨论】：

【解决方案4】：

我肯定会选择 Mike 的解决方案！更加优雅和高效。

但我看不出有什么理由不在这里使用 GROUP BY。这将使它更加优雅和高效。我建议去掉多余的“COUNT(*) OVER (PARTITION BY 1)”，而是对计数求和。

SELECT CardType 
       , COUNT(*) AS TypeCount
       , SUM(COUNT(*)) OVER () AS TotalCount
       , COUNT(*) * 1.0 / SUM(COUNT(*)) OVER () AS TypePercent
FROM Sales.CreditCard
GROUP BY CardType

注意事项：

“PARTITION BY 1”是多余的，因此省略。
计算 CardType-Counts 的 SUM 我们从数整张桌子一次再次不分区。
使用*1.0 代替强制转换。
查询未测试，但应该可以工作..

【讨论】：

【解决方案5】：

SELECT  invalidCount = (SELECT COUNT(*) FROM <...a...> WHERE <...b...>),
        unknownCount = (SELECT COUNT(*) FROM <...c...> WHERE <...d...>),
        totalCount       = (SELECT COUNT(*) FROM <...e...> WHERE <...f...>)
INTO #tmp

SELECT invalidCount,
       unknownCount,
       totalCount,
       invalidCount * 100 / totalCount AS PercentageInvalid, 
       unknownCount * 100 / totalCount AS UnknownPercentage
FROM #tmp

DROP TABLE #tmp

【讨论】：

这比“从（现有查询）中选择无效计数*100（等）”更快吗
不确定witch 是否更快，但您始终可以编写两个查询并运行并查看witch 使用SQL Profiler 是否更快