title: Do sub queries in select statement creating any performance downgrade?
body: <pre><code>select po_number,
              (select t.full_name 
               from person t 
               where t.subscriber_id=358 
                and t.company_id=2
                and person_id=p.buyer_person_id) buyer_name 
  from po_header p 
  where subscriber_id=358 and company_id=2 ;
  </code></pre>
  
  <p>Please see above example. 
  Guys could you please help me to understand the subquery performance in select statement? </p>