title: How to count common usage of items in SQL?
body: <p>I want to count how much common projects companies have with each other, like:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>Company</th>
  <th>Participation</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>Apple</td>
  <td>Project 1</td>
  </tr>
  <tr>
  <td>Microsoft</td>
  <td>Project 1</td>
  </tr>
  <tr>
  <td>Tesla</td>
  <td>Project 2</td>
  </tr>
  <tr>
  <td>Apple</td>
  <td>Project 2</td>
  </tr>
  <tr>
  <td>Microsoft</td>
  <td>Project 2</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>Is there a easy to go method in SQL to do so? With the output like that?</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th></th>
  <th>Apple</th>
  <th>Microsoft</th>
  <th>Tesla</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>Microsoft</td>
  <td>2</td>
  <td></td>
  <td>1</td>
  </tr>
  <tr>
  <td>Tesla</td>
  <td>1</td>
  <td>1</td>
  <td></td>
  </tr>
  <tr>
  <td>Apple</td>
  <td></td>
  <td>2</td>
  <td>1</td>
  </tr>
  </tbody>
  </table>
  </div>