sql - Find rows that have the same value on a column in MySQL

Question

In a [member] table, some rows have the same value for the email column.

login_id | email
---------|---------------------
john     | [email protected]
peter    | [email protected]
johnny   | [email protected]
...

Some people used a different login_id but the same email address, no unique constraint was set on this column. Now I need to find these rows and see if they should be removed.

What SQL statement should I use to find these rows? (MySQL 5)

Answer 1

This query will give you a list of email addresses and how many times they're used, with the most used addresses first.

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

If you want the full rows:

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