Выберите строки с тем же значением в столбце
select * from table where email in (
select email from table
group by email having count(*) > 1
)
Encouraging Earthworm
select * from table where email in (
select email from table
group by email having count(*) > 1
)SELECT email,
count(*) AS c
FROM TABLE
GROUP BY email
HAVING c > 1
ORDER BY c DESC