#0029

Find Duplicate Emails

EasySQL10 min10 XP

Problem

Write a query that returns each duplicate email and how many times it appears.

Duplicate detection is a practical data quality task and a very common SQL interview warm-up.

users(id, email)

Example 1

Inputa@test.com appears twice, b@test.com appears once

Outputa@test.com, 2

Only emails with count greater than 1 are duplicates.

CodeSQL

SELECT
  email,
  -- count rows
FROM users
-- group and filter duplicates

SELECT
  email,
  -- count rows
FROM users
-- group and filter duplicates

Visible browser tests run here when available.

Testcases1 visible / 4 hidden categories

One duplicate email

Inputthree users, one repeated email

Expecteda@test.com count 2

HAVING COUNT(*) > 1 keeps duplicate groups.

Hidden Test Categories

No duplicatesMultiple duplicate emailsThree or more occurrencesCase-sensitive email values