Additional fields for my entity from another table in views
Technically it's possible, using hook_views_query_alter(), you can adapt the view query to add or change conditions. So you could add a join with something like this:

function modulename_views_query_alter(&amp;$view, &amp;$query) {
  $join = new views_join();
  $join-&gt;table = 'mytable';
  $join-&gt;field = 'eid';
  $join-&gt;left_table = 'entity_table';
  $join-&gt;left_field = 'eid';
  $join-&gt;type = 'left';
  $query-&gt;add_relationship('relationship_name', $join, 'entity_table');
}


But a better approach would be to use hook_views_data() to expose your table to views, and then add the relevant fields when needed (with a relationship though), but in practical terms is no different than altering the query.