title: SQLite error 'column _id is not unique' on when inserting into an empty table
body: <p>I have a table with 4 fields: <code>_id</code>, <code>to</code>, <code>from</code>, <code>hidden</code></p>
  
  <p>Upon trying to insert the following values:</p>
  
  <pre><code>_id=167 from=1311005879000 to=1311005879000 hidden=0
  </code></pre>
  
  <p>into my table, I got an <strong>SQLiteConstraintException</strong> stating that</p>
  
  <pre><code>'column _id is not unique (code 19)'
  </code></pre>
  
  <p>To find the cause for this problem I tried querying the size of the table and found it is 0, so I have no idea where this is coming from.</p>
  
  <p>Maybe I didn't understand the error correctly?</p>
  
  <p>Edit: some code!</p>
  
  <pre><code>try {
      mDatabase.insertOrThrow("groups", null,
              mContentValues);
  } catch (SQLException e) {
      e.printStackTrace();
  }
  </code></pre>
  
  <p>Creation SQL:</p>
  
  <pre><code>CREATE TABLE IF NOT EXISTS groups(_id LONG PRIMARY KEY,hidden INTEGER,from LONG,to LONG
  </code></pre>