title: Ambiguous column name error for user_id
body: <p>My users table has the columns
  <code>user_id</code>, <code>email</code>
  My invites table has the columns
  <code>invite_id</code>  <code>request_id</code>  <code>user_id</code>                   <code>sent_time</code></p>
  
  <p>When I run the following query, I get the two tables joined into 1, which is expected.</p>
  
  <pre><code>'SELECT * FROM users INNER JOIN invites ON users.user_id = invites.user_id'
  </code></pre>
  
  <p>However, when I run the following query,</p>
  
  <pre><code>'SELECT user_id FROM users INNER JOIN invites ON users.user_id = invites.user_id'
  </code></pre>
  
  <p>I get the following error</p>
  
  <pre><code>OperationalError: (sqlite3.OperationalError) ambiguous column name: user_id [SQL: 'SELECT user_id FROM users INNER JOIN invites ON users.user_id = invites.user_id']
  </code></pre>
  
  <p>Any help appreciated.</p>