title: `Update from SubQuery` not work in Go gorm
body: <p>I would like to use below mysql update to update data.</p>
  <pre class="lang-sql prettyprint-override"><code>update goods t1, user t2 
  set t1.user_id = t2.user_id where t1.phone ? and t2.phone = ?
  </code></pre>
  <p>I am tring to use below gorm query <code>Update from SubQuery</code> to solve it,</p>
  <p><code>models.DB.Model(&amp;models.User{}).Select(&quot;user_id&quot;).Where(&quot;goods.phone = ? and users.phone = ?&quot;, row[3], row[3]))</code></p>
  <p>but subquery not work, log.Println <code>UPDATE good SET user_id = 0</code>, if I declare a user and good model as <code>users</code> and <code>goods</code> above the above code,</p>
  <pre><code>var users models.User
  var goods models.Good
  </code></pre>
  <p>I will get error of <code>users and goods declared but not used</code>, is there anyone who knows how to solve it? Thanks so much for any help.</p>