To check for duplicate records in SQL, one effective method is to utilize the `GROUP BY` clause in combination with aggregate functions such as `COUNT()`. By grouping the records based on the columns that define uniqueness, you can easily identify duplicates by applying a `HAVING` clause to filter groups with a count greater than one. For instance, if you have a table named `users` and you want to check for duplicates based on the `email` column, you would execute a query like:

“`sql
SELECT email, COUNT(*) as count
FROM users
GROUP BY email
HAVING COUNT(*) > 1;
“`
This will return all email addresses that appear more than once in the `users` table, along with the number of occurrences for each duplicate.

In cases where you need more detailed information about the actual duplicate records, you can use a Common Table Expression (CTE) or a subquery to enhance clarity. For example, you might first find the duplicates using a query similar to the one above, and then join it back with the original table to retrieve the full rows. Here’s how it can be done using a CTE:

“`sql
WITH DuplicateEmails AS (
SELECT email
FROM users
GROUP BY email
HAVING COUNT(*) > 1
)
SELECT u.*
FROM users u
JOIN DuplicateEmails d ON u.email = d.email;
“`
This approach efficiently provides you with all the details of the records that share the same email addresses, allowing for further analysis or cleanup of duplicate entries.