title: SQL: Finding non-matches
body: <p>my first table looks like the following (t1)</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>uid</th>
  <th>car_id</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>s123</td>
  <td>1234</td>
  </tr>
  <tr>
  <td>p908</td>
  <td>2345</td>
  </tr>
  <tr>
  <td>q123</td>
  <td>567</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>my second table looks like the following (t2):</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>uid</th>
  <th>category</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>s123</td>
  <td>honda</td>
  </tr>
  <tr>
  <td>p908</td>
  <td>mercedes</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>What I am trying to do is to find the uids (along with their car_id) from t1 that do not have a matching uid in t2. For example, the &quot;q123&quot; from t1 should be returned since it does not appear in t2. Any idea how this can be achieved?</p>
  <p>Thank you!</p>