在 SQL 中具有列的结果的百分比答案

【问题标题】：Percentage of results that have a column in SQL在 SQL 中具有列的结果的百分比
【发布时间】：2009-12-29 22:46:59
【问题描述】：

我正在尝试获得一个结果，该结果将显示独特的“原因”、它们的数量以及它们占总数的百分比。到目前为止我有

SELECT DISTINCT Reason, 
       COUNT(Reason) AS Number, 
       CAST(COUNT(Reason) AS float) / CAST(COUNT(*) AS float) AS percentage
FROM DeletedClients

但是，我发现 COUNT(*) 和 COUNT(Reason) 给出了相同的结果。所以我的基本问题是，当我在查询中使用 distinct 时，如何获得总行数？我使用的是 SQL Server 2005

【问题讨论】：

标签： sql select count distinct

【解决方案1】：

SELECT Reason, 
       COUNT(Reason) AS Number, 
       CAST(COUNT(Reason) AS float) / CAST(t.Total AS float) AS percentage
FROM DeletedClients,
     (SELECT COUNT(*) As Total FROM DeletedClients) t
GROUP BY Reason, Total

【讨论】：

【解决方案2】：

用途：

SELECT x.reason,
       x.num AS NUMBER,
       CONVERT(x.num, float)/(SELECT CONVERT(COUNT(*), float) FROM DELETEDCLIENTS) AS PERCENTAGE
  FROM (SELECT t.reason,
               COUNT(*) 'num'
          FROM DELETEDCLIENTS t
      GROUP BY t.reason) x

【讨论】：

这给出了 0 作为所有行的百分比。
@Brian：正确 - 整数数学。已更正。

【解决方案3】：

select reason, count(reason), 
       (count(reason)::float / (select count(reason) from reasons)::float) * 100 
       as percent 
from DeletedClients group by reason order by reason;

这就是我想出的。我以特定于 postgresql 的方式进行了转换，但您可以根据需要进行调整。您需要使用分组依据。我添加订单只是因为我喜欢它：P

【讨论】：

【解决方案4】：

我认为你应该使用 group by：


SELECT Reason, 
       COUNT(Reason) AS Number, 
       CAST(COUNT(Reason) AS float) / CAST(COUNT(*) AS float) AS percentage
FROM DeletedClients
GROUP BY Reason

【讨论】：

这导致所有行的百分比为 1 (SQL Server)

【解决方案5】：

您的查询会出现问题。没有分组依据（如果您想返回原因列，则需要它。

至于目标，COUNT（和其他聚合）忽略空值（如果您至少使用 SQL Server），所以这应该有效：

DECLARE @TOTAL FLOAT
SELECT @TOTAL = COUNT(1)
FROM DeletedClients

SELECT DISTINCT
    Reason,
    Cnt AS Number,
    @TOTAL AS TotalRecords,
    CAST(Cnt AS float) / @TOTAL AS percentage
FROM (
    SELECT
        Reason,
        COUNT(*) AS Cnt
    FROM DeletedClients
    GROUP BY Reason
) t
GROUP BY
    Reason,
    Cnt

【讨论】：