title: subqueries mysql help
body: <p>I have 3 tables in a MySql Database:</p>
  
  <ol>
  <li>User;</li>
  <li>Company that has a date field called data;</li>
  <li>Object that has idUser and idCompany.</li>
  </ol>
  
  <p>I have to retrieve Companies that has got a specific date in date field of Company, and that meet the following rule:
  There should be no records in Object table that has idP=xx and idI=(an id of a company that has got the specific value date yy-mm-dd)</p>
  
  <p>How can I write this query?</p>