title: postgreSQL - fill in blank date rows per ID
body: <p>I have a table which looks like this:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>ID</th>
  <th>money_earned</th>
  <th>days_since_start</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>1</td>
  <td>1000</td>
  <td>1</td>
  </tr>
  <tr>
  <td>1</td>
  <td>2000</td>
  <td>2</td>
  </tr>
  <tr>
  <td>1</td>
  <td>3000</td>
  <td>4</td>
  </tr>
  <tr>
  <td>1</td>
  <td>2000</td>
  <td>5</td>
  </tr>
  <tr>
  <td>2</td>
  <td>1000</td>
  <td>1</td>
  </tr>
  <tr>
  <td>2</td>
  <td>100</td>
  <td>3</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>I want that rows, without a days_since_start (which means that the money_earned column was empty that day) - will include all the days PER ID, and fill the money_earned with last known value, so it to look like this:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>ID</th>
  <th>money_earned</th>
  <th>days_since_start</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>1</td>
  <td>1000</td>
  <td>1</td>
  </tr>
  <tr>
  <td>1</td>
  <td>2000</td>
  <td>2</td>
  </tr>
  <tr>
  <td>1</td>
  <td><strong>2000</strong></td>
  <td><strong>3</strong></td>
  </tr>
  <tr>
  <td>1</td>
  <td>3000</td>
  <td>4</td>
  </tr>
  <tr>
  <td>1</td>
  <td>2000</td>
  <td>5</td>
  </tr>
  <tr>
  <td>2</td>
  <td>1000</td>
  <td>1</td>
  </tr>
  <tr>
  <td>2</td>
  <td><strong>1000</strong></td>
  <td><strong>2</strong></td>
  </tr>
  <tr>
  <td>2</td>
  <td>100</td>
  <td>3</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>I have tried to look up for something like that, but I don't even know what function does that...</p>
  <p>thank you!</p>