title: Implement Foreign Key in mysql table
body: <p>Im trying to restore some old database tables, that when i build them i did not user foreign keys. I have the field that corresponds to the Foreign Key, but i've not set it up in the relations table to which table it connected.</p>
  
  <p>Right know i have a problem because if i try to add that relation, it cannot, because there are some rows deleted in the other table.</p>
  
  <p>Is there any mysql command for checking this type NULL relations for me to delete the rows that i dont need.. and in the end.. add the relation.</p>
  
  <pre>
  TableA
      id,
      name
  
  TableB
     id,
     tableA_id,
     points
  </pre>
  
  <p>I've deleted some TableA rows.. now i cannot had that relation.</p>
  
  <p>Any mysql command to help, or need to check manually?</p>
  
  <p>Thanks</p>