 <p>The keyword DISTINCT is used to eliminate duplicate rows from a query result:</p> <pre><code>SELECT DISTINCT ... FROM A JOIN B ON ... </code></pre> <p>However, you can sometimes (possibly even 'often', but not always) avoid the need for it if the tables are organized correctly and you are joining correctly.</p> <p>To get more information, you are going to have to ask your question more clearly, with concrete examples.</p>