title: Unknown column 'user.id' in 'on clause'
body: <p>MySQL query:</p>
  
  <pre class="lang-sql prettyprint-override"><code>SELECT 
      *, 
      `message`.`status` as `message_status`, 
      `message`.`id` as `message_id`, 
      group_concat(response.response) as response, 
      group_concat(response.id) as response_id, 
      `message`.`user_id` as `sender` 
  FROM `message` 
  LEFT JOIN `pet_info` ON `pet_info`.`id` = `message`.`pet_id` 
  LEFT JOIN `response` ON `response`.`message_id` = `message`.`id` 
  LEFT JOIN `user` as sender ON `user`.`id` = `message`.`user_id` 
  LEFT JOIN `user` as receiver ON `user`.`id` = `message`.`owner_id` 
  WHERE `user_id` = '6' 
  AND `pet_id` = '6' 
  GROUP BY `message`.`id`
  </code></pre>
  
  <p>How can I resolve this error?</p>