title: Selecting one celd in the column result from SQL with PDO
body: <p>I have this situation after my SQL stament: One single column with the same result. For example, the age of all people with blue eyes and green jeans, will return me one column "age" with the result for example 50 years (because all people with this characteristics have 50), repeted as many time as there are people with this parameters in the DB. </p>
  
  <p>How I can do in <code>PDO</code> (or <code>SQL</code>) to filter or to get only one result, or only one fild (50)? 
  I try: <code>fetchAll(PDO::FETCH_ASSOC)</code> and <code>fetchColumn()</code> but both return a array or nothing</p>