(safe) page for entering image url information

<?php
 // session, formatting, etc.
 include('header.php');

 // connect to database, DRY (Dont Repeat Yourself) code
 include('db.php');

 // is there a post?
 if( isset($_POST['title']) AND isset($_POST['url']) )
  {
    if( $_POST['title']<>'' AND $_POST['url']<>'')
    {
      // assign title and url variables
      $title=$_POST['title'];
      $url=$_POST['url'];

     // validation, sanitation
     // is $url an url?... etc.
     // is $title a string?... etc.

      // escaping
     $title=mysqli_real_escape_string($conn,$title);
     $url=mysqli_real_escape_string($conn,$url);

      // the insert query
     $sql_insert = "INSERT INTO urls (id, title, url) VALUES (NULL, '$title', '$url')";
       echo $sql_insert . "<br>";
      // insert image into database:
      if(mysqli_query($conn, $sql_insert))
      {
        echo "string stored successfully";
      } else {
        printf("Error message: %s\n", mysqli_error($conn));
      }
    } else {
      echo 'All the fields are required<br>';
    }
  }

  // show the form.
 ?>
 <!DOCTYPE html>
 <html lang="en">
 <head>
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <meta http-equiv="X-UA-Compatible" content="ie=edge">
   <title>Escaped entries</title>
 </head>
 <body>

 </body>
 </html>
  <form action="form.php" method="post" >
    <label for="">title</label>
    <input type="text" name="title" REQUIRED AUTOFOCUS ><br>

    <label for="">URL</label>
    <input type="text" name="url" REQUIRED ><br>

    <input type="submit" value="submit" >
  </form>