How to find duplicate email within a mysql table

If you want to output the data exactly like shown in your question, use this query:

SELECT email, COUNT(*) AS count
FROM table
GROUP BY email HAVING count > 0
ORDER BY count DESC;

You can't directly do that in MySQL because there is no function to urlencode or urldecode strings.

You will have to create a User Defined Function to handle that process. Once you have that function just go for a simple group by with a having clause.

Link to the required UDFs

If UDFs are not an option, the only workaround I can think of is manually replacing the chars (under your own risk):

SELECT REPLACE(email, "%40", "@") DuplicateEmail, COUNT(*) Amount
FROM t
GROUP BY DuplicateEmail
ORDER BY Amount desc

Fiddle here.

Output:

| DUPLICATEEMAIL | AMOUNT |
---------------------------
|  [email protected] |      2 |
| [email protected] |      2 |
|  [email protected] |      1 |

Here is a simple solution:

SELECT email, COUNT(1) FROM table_name GROUP BY email HAVING COUNT(1) > 1