尝试使用函数调用sql查询时的警告消息和通知

    $unitname = "";

    function display($unitname) {
    $unitname = "";

    $conn = mysqli_connect('localhost', 'root', '', 'registration');
    if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
    }

    $sql = "SELECT unitname from UNIT";
    $result = $conn->query($sql);
      if ($result->num_rows > 0) {
        while ($row = $result->fetch_assoc()) {
        echo "<br>Unit Name:" . $unitname["unitname"] . "<br>";
        }
      } else {
    echo "0 results";
   }
    return $unitname;
   }

  ?>