title: How to relate 3 tables depending on event
body: <p>I have a table that have information about different types of events that can be done by persons in two categories <strong>civil and worker</strong></p>
  
  <p>so for each one of them I have their respective tables</p>
  
  <pre><code>civil{  civil_id, name, age,telephone...} the  primary key is civil_id
  
  worker{ worker_id, name, duty, department...} the  primary key is worker_id
  </code></pre>
  
  <p>then the event table has a list of all possible events</p>
  
  <pre><code>event {type_of_event} the  primary key is type_of_event
  </code></pre>
  
  <p>then I am planing to store information in other table </p>
  
  <p>with eventype, the person that did the job (worker or civil)</p>
  
  <pre><code>id  event_type       date      person
  -----------------------------------
  1   type1         12-12-12     x 
  2   type1         05-12-10     y
  3   type2         02-12-12     y
  </code></pre>
  
  <p>Now in this design I do not know how to relate whose person did the job if, I would had only a kind of person (aka civil) i would only store the civil_id in person field in this last table....but how to know if it was civil or worker, do I need other intermediate table?</p>