title: In Oracle/SQL how to select rows with same column id but a different value for non-id column
body: <p>In the table below, I want to show every <strong>user_id</strong> that shows up with both a 0 and a 1 in the <strong>is_logged_in</strong> flag.</p>
  
  <pre><code>__________________________
  | user_id | is_logged_in |
  +------------------------+
  |    A    |      1       |
  +------------------------+
  |    B    |      1       |
  +------------------------+
  |    B    |      0       |
  +------------------------+
  |    C    |      0       |
  +------------------------+
  |    D    |      0       |
  +------------------------+
  |    D    |      1       |
  +------------------------+
  |    C    |      0       |
  +------------------------+
  </code></pre>
  
  <p>Can it be done without a GROUP BY condition? If possible, can you also show me how to query without GROUP BY. Thanks SO.</p>
  
  <p>Result after query:</p>
  
  <pre><code>___________
  | user_id |
  +---------+
  |    B    |
  +---------+
  |    D    |
  +---------+
  </code></pre>