title: Yii2: ActiveRecord with distinct query
body: <p>I need to write an ActiveRecord query where I get all fields of rows without duplicates in one field.</p>
  
  <p>Example: Here is a table of books. I want to get all data of the rows with
  distinct isbn. From duplicates the first row should be taken. The result should be the rows with id 1,2,4</p>
  
  <pre><code>id  | title   | isbn
  --- | ------- | ------
  1   | hello   | 1001
  2   | world   | 1002
  3   | this    | 1002
  4   | is      | 1003
  5   | funny   | 1003
  </code></pre>
  
  <p>My first attempt was</p>
  
  <pre><code>$books = Books::find()-&gt;select('isbn')-&gt;distinct()-&gt;all();
  </code></pre>
  
  <p>but that fills only the isbn field in <code>$books[0], $books[1], ...</code>.</p>
  
  <p>Is this possible using Yii2 ActiveRecord?</p>