Как добавить поиск по таблице mysql + php

Сортировку сделал не получается добавить поиск по таблице, подскажите

 $mysqli = NEW mysqli('localhost', 'root', '', 'db_dolphin');
if (isset($_GET['order'])) {
  $order = $_GET['order'];
}else{
  $order = 'vacancy_salary';
}
if (isset($_GET['sort'])) {
  $sort = $_GET['sort'];
}else{
  $sort = 'ASC';
}
$resultSet = $mysqli->query("SELECT * FROM vacancies ORDER BY $order $sort");
if ($resultSet->num_rows > 0) {
  $sort == 'DESC' ? $sort = 'ASC' : $sort = 'DESC';
  echo "
  <table class='table table-bordered table-hover table-striped' style='table-layout: fixed'>
    <tr>
      <th><a href='?order=vacancy_position&&sort=$sort'>Position</a></th>
      <th></th>
      <th><a href='?order=vacancy_vessel_type&&sort=$sort'>Type of vessel</a></th>
      <th><a href='?order=vacancy_salary&&sort=$sort'>Salary per month</a></th>
      <th><a href='?order=vacancy_join_date&&sort=$sort'>Join date</a></th>
      <th><a href='?order=vacancy_duration&&sort=$sort'>Duration</a></th>
      <th><a href='?order=vacancy_company&&sort=$sort'>Company name</a></th>
      ";
      while ($rows = $resultSet->fetch_assoc())
      {
        $vacancy_position = $rows['vacancy_position'];
        $vacancy_vessel_type = $rows['vacancy_vessel_type'];
        $vacancy_salary = $rows['vacancy_salary'];
        $vacancy_join_date = $rows['vacancy_join_date'];
        $vacancy_duration = $rows['vacancy_duration'];
        $vacancy_company = $rows['vacancy_company'];
        echo "
        <tr>
          <td>$vacancy_position</td>
          <td>on</td>
          <td>$vacancy_vessel_type</td>
          <td>$vacancy_salary</td>
          <td>$vacancy_join_date</td>
          <td>$vacancy_duration</td>
          <td>$vacancy_company</td>

        </tr>
        ";
      }
      echo "</table>";
    }else{
      echo "No records returned.";
    }