The SQL DISTINCT clause is used together with the SQL SELECT keyword, to return a dataset with unique entries for certain database table column.
SELECT DISTINCT LastName FROM Customers
SELECT DISTINCT(id_email), email_name, email FROM emails LEFT JOIN emails_lists ON emails.id_email = emails_lists.fk_email WHERE email_valid = 1 AND fk_list IN ($fk_list)
Here's a handy query for finding duplicates in a table. Suppose you want to find all email addresses in a table that exist more than once:
SELECT email, COUNT(email) AS NumOccurrences FROM users GROUP BY email HAVING ( COUNT(email) > 1 )
You could also use this technique to find rows that occur exactly once:
SELECT email FROM users GROUP BY email HAVING ( COUNT(email) = 1 )