每组不同的 SQL 计数除以总数的不同计数答案

【问题标题】：SQL count distinct per group divided by count distinct of total每组不同的 SQL 计数除以总数的不同计数
【发布时间】：2021-05-09 13:40:08
【问题描述】：

我有：

id	value
1	123
1	124
1	125
2	126
2	127
2	127
3	128
3	128
3	128

我想要一个像这样的聚合：

id	distinct_count	total_distinct	percentage
1	3	6	0.5
2	2	6	0.33
3	1	6	0.167

我尝试应用这样的窗口覆盖子句：

SELECT id,
       COUNT(DISTINCT value) AS distinct_count,
       COUNT(DISTINCT value) OVER () AS total_distinct,
       COUNT(DISTINCT value) / COUNT(DISTINCT value) OVER () AS percentage
FROM have
GROUP BY id

但它似乎还没有实现。

有没有办法在没有连接的情况下实现这一点？

【问题讨论】：

你得到了什么结果？
我遇到了一个错误.. 尚不支持窗口函数参数中的 DISTINCT
将此 SO 视为有效的 SUM 聚合示例：stackoverflow.com/questions/46909494/…
为什么要问这个问题？如果你能在 10 分钟内自己找到答案？
不确定你的意思@Luuk。我找不到答案，因此 q

标签： sql distinct

【解决方案1】：

你可以这样做：

SELECT id,
       COUNT(DISTINCT value) AS distinct_count,
       (SELECT COUNT(DISTINCT value) FROM have) AS total_distinct,
       (0.0+COUNT(DISTINCT value)) / (SELECT COUNT(DISTINCT value) FROM have) AS percentage
FROM have
GROUP BY id

或者做：

WITH cte AS (SELECT COUNT(DISTINCT value) AS value FROM have)
SELECT 
       id,
       COUNT(DISTINCT value) AS distinct_count,
       cte.value AS total_distinct,
       (0.0+COUNT(DISTINCT value)) / cte.value AS percentage
FROM have
CROSS APPLY cte
GROUP By cte.value,id;

【讨论】：

谢谢！由于某种原因过于关注 OVER 子句

【解决方案2】：

另一种方法是枚举值并使用条件聚合：

SELECT id,
       SUM(CASE WHEN seqnum_iv = 1 THEN 1 ELSE 0 END) as distinct_count,
       SUM(CASE WHEN seqnum_v = 1 THEN 1 ELSE 0 END) as total_distinct_count,
       (SUM(CASE WHEN seqnum_iv = 1 THEN 1.0 ELSE 0 END) /
        SUM(CASE WHEN seqnum_v = 1 THEN 1.0 ELSE 0 END)
       ) as ratio
FROM (SELECT h.*,
             ROW_NUMBER() OVER (PARTITION BY id, value ORDER BY value) as seqnum_iv,
             ROW_NUMBER() OVER (PARTITION BY value ORDER BY value) as seqnum_v
      FROM have h
     ) h
GROUP BY id;

这可能比使用子查询的方法更快。

【讨论】：

谢谢，我会比较运行时，因为它是在大型事务数据上。
@Grizzly2501 。 . .我第一次回答时错过了一些东西。我已经确定了答案。