select rows where column contains same data in more than one record
HAVING is a great aggregate filter. (http://dev.mysql.com/doc/refman/5.6/en/group-by-extensions.html) For example, select the article_titles with more than on occurrence:

SELECT count(*), article_title
FROM articles
GROUP BY article_title
HAVING COUNT(*) &gt; 1;


Adding columns to the SELECT and GROUP BY clauses allow you to locate duplicates based on a composite key of multiple columns.