Vind dubbelle records

Voorbeeld voor vinden van dubbele email adressen:

SELECT email, 
 COUNT(email) AS NumOccurrences
FROM users
GROUP BY email
HAVING ( COUNT(email) > 1 )

Of vind de e-mail adressen met 1 occurance:

SELECT email
FROM users
GROUP BY email
HAVING ( COUNT(email) = 1 )