Approach I: Using
GROUP BY and a temporary table [Accepted]
Duplicated emails existed more than one time. To count the times each email exists, we can use the following code.
select Email, count(Email) as num from Person group by Email;
| Email | num | |---------|-----| | email@example.com | 2 | | firstname.lastname@example.org | 1 |
Taking this as a temporary table, we can get a solution as below.
select Email from ( select Email, count(Email) as num from Person group by Email ) as statistic where num > 1 ;
Approach II: Using
GROUP BY and
HAVING condition [Accepted]
A more common used way to add a condition to a
GROUP BY is to use the
HAVING clause, which is much simpler and more efficient.
So we can rewrite the above solution to this one.
select Email from Person group by Email having count(Email) > 1;