Question

I am using the following query to select emails that are duplicates:

SELECT email
                FROM contacts
                WHERE active = 1
                GROUP BY email
                HAVING ( COUNT(email) > 1)

In the case above, if two users have the same email, that query will show them. However, there is another email field named email2, what can I do so that I compare the count among many email fields? (So, for example, if a user has email equal to email2 of another user, they will be considered duplicates)

Thank you!

Answer 1

SELECT tmp.email FROM (
    SELECT email as email FROM contacts WHERE active = 1
    UNION ALL
    SELECT email2 as email FROM contacts WHERE email != email2 AND active = 1
) as tmp
GROUP by tmp.email
HAVING COUNT(tmp.email) > 1

P.S : my syntax could be wrong, but the idea should be something like this.