How do I add another mysqli query into a while loop?

Question

So I am carrying out a query and returning the results in the form of a table. The code below works well.

        <table>
      <thead>
        <tr style="text-align: center;">
          <th>Activity</th>
          <th>Description</th>
          <th>Frequency</th>
          <th>Mandatory</th>
          <th>Added Yet</th>
        </tr>
      </thead>
      <tbody>
        <?php
          $stmt = $conn->prepare("SELECT * FROM knowledgebase ORDER BY category ASC");
          $stmt->execute();
          $result = $stmt->get_result();
          if($result->num_rows === 0) echo "<tr><td>No activities found</td><td></td><td></td><td></td><td></td><td></td></tr>           </tbody>
                  </table></br></br>
          Why not add your first activity from our <a href=\"#\">Knowledge base</a> or <a href=\"create_activities.php\">create a new activity</a> of your own";
          else {
          while($row = mysqli_fetch_array($result)) {
              $activity_id          =   $row['id'];
              $title                =   $row['title'];
              $description          =   $row['description'];
              $frequency            =   $row['frequency'];
              $mandatory            =   $row['mandatory'];

              echo "<tr><td><a href=\"add_activities.php?id=".$activity_id."\">".$title."</a></td><td>".$description."</td><td style=\"text-align: center;\">".$frequency."</td><td style=\"text-align: center;\">".$mandatory."</td><td></td></tr>";
            }
          }
           $stmt->close();
         ?>
      </tbody>
    </table>

What I want to add in is another query inside the final <td></td> . What I want to do is query a second db table and say if this activity has already been added to the users table, echo YES, otherwise, echo NO .

The problems is, adding the query into the while loop keeps throwing errors.

Any suggestions gratefully received.

Answer 1

Instead of running another query for every row, you could join the users table to the knowledgebase table in your first query. If you use a left join, you'll still get all the rows from knowledgebase.

SELECT knowledgebase.*, userstable.activity_id
FROM knowledgebase
     LEFT JOIN userstable ON knowledgebase.id = userstable.activity_id
ORDER BY category ASC

Then in your last <td> , you can print YES/NO depending on whether or not there was a matching row in the users table.

...<td><?php echo $row['activity_id'] ? 'YES' : 'NO' ?></td>...

(I made up names for your other table and column, but I think it shows the general idea.)