SELECT a.*, b.totalCount AS Duplicate
FROM tablename a
INNER JOIN
(
SELECT email, COUNT(*) totalCount
FROM tableName
GROUP BY email
) b ON a.email = b.email
WHERE b.totalCount >= 2
for bedre ydeevne skal du tilføje en INDEX
i kolonne EMail
.
ELLER
SELECT a.*, b.totalCount AS Duplicate
FROM tablename a
INNER JOIN
(
SELECT email, COUNT(*) totalCount
FROM tableName
GROUP BY email
HAVING COUNT(*) >= 2
) b ON a.email = b.email