if(isset($_POST['id']))
{
     // id to search
     $id = $_POST['id'];

     // Fetch Data From DataBase
     $sql ="SELECT * , DATE_FORMAT(birthdate, '%d/%m/%Y') AS birthdate FROM `personal_info`  WHERE `personal_id_number` = $id ORDER BY birthdate DESC";

     $result = $conn -> query($sql);

     if ($result -> num_rows <> 0) {
         while ( $row = $result -> fetch_assoc() ) {
             echo "<tr><td>" . $row["person_name"]
                  . "</td><td>". $row["personal_id_number"]
                  . "</td><td>". $row["birthday"]
                  . "</td><td>" . $row["adress"]
                  . "</td><td>" . $row["phone_number"]
                  . "</td><td>" . $row["email"]
                  . "</td><td colspan='3' class='more fit'>"
                  . $row["more_info"]
                  . "</td></tr>";
          }
     }

只有当搜索条件是数据库中有数字的某个字段时，这个搜索字段才起作用，比如“个人id”和“电话号码”。
否则，如果我把“personal\u name”作为搜索条件，我会得到一个错误“notice:trying to get property'num\u rows'of non object”。