按输入选择搜索

如何在我的网站上搜索这样的;如果访问者选择输入用户名，表只显示用户名、id或性别。

我想我应该添加一些东西而不是*，但我找不到。你能帮我吗?

foreach($db->query('SELECT * FROM uyeler ORDER BY RAND()LIMIT 20') as $row)

<div class="body">
<div class="table"
        <select>
          <option value="id">ID</option>
          <option value="user">Username</option>
          <option value="sex">Sex</option>
          <option value="country">Country</option>            
          <option value="age">Age</option>
          <option value="twitter">Twitter</option>
          <option value="instagram">Instagram</option>            
          <option value="snapchat">Snapchat</option>
       </select>
            <input type="text" name="searchbox">
            <input type="submit" value="Search"><input type="submit" value="Refresh"></br></br>
        <table align=center width="1200">
          <tr>
            <th>ID</th>
            <th>Username</th>
            <th>Sex</th>
            <th>Country</th>
            <th>Age</th>
            <th>Twitter</th>
            <th>Instagram</th>
            <th>Snapchat</th>
            <th>Details</th>
        </tr>
        <?php
        foreach($db->query('SELECT * FROM uyeler ORDER BY RAND()LIMIT 20') as $row) {
                echo "<tr><td>" .$row['id'] . "</td>";
                echo "<td>" .$row['username'] . "</td>";
                echo "<td>" .$row['sex'] . "</td>";
                echo "<td>" .$row['country'] . "</td>";
                echo "<td>" .$row['age'] . "</td>";
                echo "<td>" .$row['twitter'] . "</td>";
                echo "<td>" .$row['instagram'] . "</td>";
                echo "<td>" .$row['snapchat'] . "</td>";
                echo ('<td><a href="details.php?id=' .$row['id'] . '" title="Panel">Details</a></td>');
                echo "</tr>";
            }
        ?>
</table>
</div>