SQL 用于查找属于某个类别的一组数据的媒体的查询

Question

我有一个 table 包含不同类别的分箱数据，例如：

category, bin, frequency
a, 0, 10
a, 1, 20
a, 2, 30
a, 3, 15
b, 0, 18
b, 1, 54
b, 2, 33
b, 3, 24

我需要找到每个类别的近似值中位数。为此，我想计算每个类别的累积百分比直方图，并将第一个值设为 50% 以上。我知道如何为一个类别执行此操作：

SELECT category, bin as approx_median
FROM (
SELECT category, bin, frequency,
    (SELECT SUM(frequency) FROM table sub WHERE sub.bin <= base.bin) 
    / (SELECT SUM(frequency) FROM table) 
    * 100 as running_percent    
FROM table base
WHERE category = a
ORDER BY bin ) p
WHERE p.running_percent >= 50.0
LIMIT 1

问题是，如何对所有类别执行此操作以获得结果

category, approx_median
a, 2
b, 1

感谢任何建议。

Answer 1

可以用IN运算符，不知道行不行。试试吧。

SELECT category, bin as approx_median
FROM (
SELECT category, bin, frequency,
    (SELECT SUM(frequency) FROM table sub WHERE sub.bin <= base.bin) 
    / (SELECT SUM(frequency) FROM table) 
    * 100 as running_percent    
FROM table base
WHERE category in (select distinct category from table)
ORDER BY bin ) p
WHERE p.running_percent >= 50.0
LIMIT 1

Answer 2

如果您发布的查询符合您的实际要求，那么只需删除条件 WHERE category = a 并试一试。无论如何，您的 running_percent 计算是基于 bin 列的。您可以按类别进一步订购您的外部查询，以使其看起来不错。

Answer 3

您可能想要做的是这样的事情：

SELECT category, Min(bin) As approx_median
FROM(
    SELECT base.category, 
    base.bin, 
    (SELECT SUM(sub.frequency) AS SummeBin FROM [table] sub WHERE sub.bin <= base.bin and sub.category = base.category)
    / (SELECT SUM(sub.frequency) FROM [table] sub WHERE sub.category = base.category GROUP BY sub.category) * 100 as running_percent 
    FROM [table] base
) p
WHERE running_percent >= 50.0
GROUP BY category

您需要对类别进行分组并在聚合中引用它。如果您使用 SQL Server 2012 及更高版本，则可以使用 Window 函数。 ABC-Analysis with Window Function.

的示例

SQL 用于查找属于某个类别的一组数据的媒体的查询

SQL query for finding the media of a set of data belonging to a category

mysql

sql