title: Reference different tables depending on a condition
body: <p>I have a table <code>[Advertiser]</code> and a table <code>[Ad]</code> that has a <code>N..M</code> relationship that an <code>Advertiser</code> can have many <code>Ads</code> so that <code>[Ad]</code> will have a column referncing <code>[Advertiser]</code>.</p>
  <p>An <code>Advertiser</code> can either be a <strong>company</strong> or a <strong>person</strong> and the data entered into the table will differ depending. So my thought was that I should split up the <code>[Advertiser]</code> table into two tables like <code>[CompanyAdvertiser]</code> and <code>[PersonAdvertiser]</code>.</p>
  <p>Is it then possible to have a column in <code>[Ad]</code> having a reference to either <code>[CompanyAdvertiser]</code> or <code>[PersonAdvertiser]</code> depending on who should be the <code>Advertiser</code>?</p>