请使用pdo或mysqli。我刚刚编辑了您现有的代码，以便您在成功插入后重定向到成功页面。

$con=mysqli_connect("localhost","root","","vdl");
    $i = 0;
    // Check connection
    if (mysqli_connect_errno())
    {
        echo "Failed to connect to MySQL: " . mysqli_connect_error();
    }
    if(isset($_POST['submit'])){ // Fetching variables of the form which travels in URL
        $company_name = $_POST['company_name'];
        $since = $_POST['since'];
        $strength = $_POST['strength'];
        $head_quarter = $_POST['head_quarter'];
        if($company_name !=''||$since !=''){
            mysqli_query($con,"insert into digital_library(company_name, since, strength, head_quarter) values ('$company_name', '$since', '$strength', '$head_quarter')");
            echo "<br/><br/><span>Data Inserted successfully...!!</span>";
            mysqli_close($con);
        }
        else{
            $i++;
        }
    }
    if($i==0){
    header("Location: success.html");
    }else{
        echo "Error msg";
    }

$con=mysqli_connect("localhost","root","","libro");
// Check connection
if (mysqli_error($con))
  {
      echo "Failed to connect to MySQL: " . mysqli_error($con);
      exit();
  }
if(isset($_POST['submit'])){ // Fetching variables of the form which travels in URL
        $company_name = $_POST['company_name'];
        $since = $_POST['since'];
        $strength = $_POST['strength'];
        $head_quarter = $_POST['head_quarter'];
        if($company_name !== ''||$since !== ''){
        mysqli_query($con,"insert into digital_library(company_name, since, strength, head_quarter) values ('$company_name', '$since', '$strength', '$head_quarter')");
    echo "<br/><br/><span>Data Inserted successfully...!!</span>";
            header("Location: success.html");
            exit();
        }
    else{
        echo "<p>Insertion Failed <br/> Some Fields are Blank....!!</p>";
        exit();
    }
}