Find Duplicate Values With GROUP BY And HAVING

Group rows by the candidate key and keep only values that appear more than once.

5/5 supported engines validation-green 1 example 2 scenarios

Docker-validated Not currently validation-green

Example 1

List email addresses that appear more than once

[email protected] appears only once, so it is filtered out by the HAVING clause. Ada and Bob each appear twice, so they are the values flagged as duplicates.

Source table data Rows loaded before the example query runs.

Setup

CREATE TABLE users (id INT, email VARCHAR(100));

INSERT INTO
  users (id, email)
VALUES
  (1, '[email protected]'),
  (2, '[email protected]'),
  (3, '[email protected]'),
  (4, '[email protected]'),
  (5, '[email protected]');

Validated query Shared across supported engines.

SQL

SELECT
  email,
  COUNT(*) AS duplicate_count
FROM
  users
GROUP BY
  email
HAVING
  COUNT(*) > 1
ORDER BY
  email;

Expected result Returned rows for the shared example.

email	duplicate_count
[email protected]	2
[email protected]	2

All engines use the same `GROUP BY` plus `HAVING COUNT(*) > 1` duplicate check here.

Useful when

Where this command helps.

checking whether imported identifiers were loaded twice
finding repeated emails, usernames, or lookup values before cleanup

Explanation

What the command is doing.

Duplicate detection usually starts with a GROUP BY on the value that should be unique, followed by HAVING COUNT(*) > 1. That pattern shows which values are duplicated and how many times they appear. It is the fastest way to audit imports, email addresses, external IDs, or any field that should not repeat.

Find Duplicate Values With GROUP BY And HAVING

List email addresses that appear more than once

Where this command helps.

What the command is doing.

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