电子邮件重复百分比计算

Question

我有一张像下面这样的表格

email            table_name
a@mail.com         a1
a@mail.com         b2
b@mail.com         a1
c@mail.com         c1
d@mail.com         d1
e@mail.com         e
g@mail.com         e
g@mail.com         e
e@mail.com         f
g@mail.com         g

那么从这里我如何计算每个表的电子邮件重复百分比

table_name total_email  duplicate_email  duplicate_percentage
a1           2                1             50%
b2           1                1             100%
c1           1                0             0
d1           1                0             0
e            2                2             100%
f            1                1             100%
g            1                1             100%

Answer 1

这是我的尝试。设置：

DECLARE @Test TABLE (
    email VARCHAR(100),
    table_name VARCHAR(100))

INSERT INTO @Test (
    email,
    table_name)
VALUES
    ('a@mail.com', 'a1'),
    ('a@mail.com', 'b2'),
    ('b@mail.com', 'a1'),
    ('c@mail.com', 'c1'),
    ('d@mail.com', 'd1'),
    ('e@mail.com', 'e'),
    ('g@mail.com', 'e'),
    ('g@mail.com', 'e'),
    ('e@mail.com', 'f'),
    ('g@mail.com', 'g')

解决方案：

;WITH DupDetail AS
(
    SELECT
        T.email,
        T.table_name,
        IsDup = CASE WHEN COUNT(*) OVER (PARTITION BY T.email) > 1 THEN 1 ELSE 0 END
    FROM
        @Test AS T
),
DupStats AS
(
    SELECT
        T.table_name,
        total_email = COUNT(DISTINCT(T.email)),
        duplicate_email = COUNT(DISTINCT(CASE WHEN T.IsDup = 1 THEN T.email END))
    FROM
        DupDetail AS T
    GROUP BY
        T.table_name
)
SELECT
    D.table_name,
    D.total_email,
    D.duplicate_email,
    duplicate_percentage = CONVERT(
        DECIMAL(5,2), 
        D.duplicate_email * 100.0 / D.total_email)
FROM
    DupStats AS D

IsDup 列将邮件标记为 1，如果它在任何表中重复，那么对于所有表中重复但按每个表分组的所有电子邮件，duplicate_email 是 COUNT DISTINCT名字。

结果：

table_name  total_email duplicate_email duplicate_percentage
a1          2           1               50.00
b2          1           1               100.00
c1          1           0               0.00
d1          1           0               0.00
e           2           2               100.00
f           1           1               100.00
g           1           1               100.00

Answer 2

你可以使用窗口函数，然后聚合：

select 
    table_name,
    sum(cnt1) duplicate,
    sum(1.0 * cnt1) / cnt2 percentage
from (
    select
        t.*,
        count(*) over(partition by email) - 1 cnt1,
        count(*) over(partition by table_name) cnt2
    from mytable t
) t
group by table_name, cnt2
order by table_name

Demo on DB Fiddle：

表名 |重复 |百分比 :--------- | --------: | :--------- a1 | 1 | 0.500000 b2 | 1 | 1.000000 c1 | 0 | 0.000000 d1 | 0 | 0.000000