Question

我有一个users表和一个emails表。用户可以收到很多电子邮件。

我想只抓住那些拥有多封电子邮件的用户。以下是我到目前为止的情况：

SELECT Users.name, emails.email
FROM Users
INNER JOIN emails
On Users.id=Emails.user_id
/*specify condition to only grab duplicates here */

Answer 1

SELECT u.id
FROM Users u
INNER JOIN emails e On u.id = e.user_id
group by u.id 
having count(distinct e.email) > 1

使用group by和having

Answer 2

您也可以使用CTE：

;WITH CTE AS (
SELECT Users.name, emails.email, ROW_NUMBER() OVER (PARTITION BY emails.email ORDER BY emails.email) AS 'Rank' 
FROM Users
INNER JOIN emails
On Users.id=Emails.user_id)
SELECT * FROM CTE WHERE Rank > 1

Answer 3

您必须计算单个子查询中的电子邮件总数，该子查询返回具有多个电子邮件的用户的user_id。

SELECT users.name, emails.email
FROM users
INNER JOIN emails
ON users.id = emails.user_id
INNER JOIN (
    SELECT user_id
    FROM emails
    GROUP BY user_id
    HAVING count(*) > 1
) _cc
ON users.id = _cc.user_id;

更新：如果您只需要user_id而不需要额外的电子邮件，则可以使用：

SELECT DISTINCT(emails.user_id)
FROM users
INNER JOIN emails
ON users.id = emails.user_id
INNER JOIN (
    SELECT user_id
    FROM emails
    GROUP BY user_id
    HAVING count(*) > 1
) _cc
ON users.id = _cc.user_id;

假设我们有以下数据：

USERS
id name
1  A
2  B
3  C
4  D
5  E

EMAILS
id user_id email
1  1       email 1
2  1       email 2
3  2       email 3
4  2       email 2
5  3       email 5

因此，使用上述数据，两个查询的结果将是：

QUERY 1

name email
A    email 1
A    email 2
B    email 3
B    email 4

QUERY 2

user_id
1
2

Answer 4

试试这个。您正在通过电子邮件进行分组，并显示那些有计数＆gt; 1

SELECT Users.name, emails.email
FROM Users
INNER JOIN emails
On Users.id=Emails.user_id 

GROUP BY emails.email HAVING COUNT(*) > 1

内部联接后仅返回重复记录

4 个答案: