查找MySQL中列上具有相同值的行

Question

在[member]表中,某些行具有相同的email列值.

login_id | email
---------|---------------------
john     | john123@hotmail.com
peter    | peter456@gmail.com
johnny   | john123@hotmail.com
...

有些人使用不同的login_id但是使用相同的电子邮件地址,此列上没有设置唯一约束.现在我需要找到这些行,看看是否应该删除它们.

我应该使用什么SQL语句来查找这些行？(MySQL 5)

Answer 1

此查询将为您提供电子邮件地址列表及其使用次数,首先使用最常用的地址.

SELECT email,
       count(*) AS c
FROM TABLE
GROUP BY email
HAVING c > 1
ORDER BY c DESC

如果你想要完整的行:

select * from table where email in (
    select email from table
    group by email having count(*) > 1
)

Answer 2

select email from mytable group by email having count(*) >1

Answer 3

这是查询email用于多于一个的查询login_id:

SELECT email
FROM table
GROUP BY email
HAVING count(*) > 1

您将需要第二个(嵌套的)查询来获取login_idby的列表email.

Answer 4

接受的答案的第一部分不适用于MSSQL.
这对我有用:

select email, COUNT(*) as C from table 
group by email having COUNT(*) >1 order by C desc

Answer 5

如果您的电子邮件列包含空值，请使用此选项

 select * from table where email in (
    select email from table group by email having count(*) > 1 and email != ''
    )