How to insert multi radio button value in database using php

<?php
include "db_connection.php";
session_start();
if (!$_SESSION['username']) {
  header("location:login.php");
}
else{
 include"inc/header.php";
 include"inc/leftsidebar.php";
 

$cat = implode(',', $_POST['cat']);

$tag = implode(',', $_POST['tag']);


 if (isset($_POST['submit'])) {
  $title=$_POST['title'];
  $content=$_POST['editor1'];
  
  $fileupload= 'img/videoarea/'.$_FILES['image']['name'];
  $fileuploadTMP= $_FILES['image']['tmp_name'];



  move_uploaded_file($fileuploadTMP, $fileupload);

  $sql="INSERT INTO `blog`(`title`, `img`, `content`, `cat`, `tag`) VALUES('$title', '$fileupload', '$content', '$cat', '$tag')";


  if (mysqli_query($conn, $sql)) {

   echo "New record created successfully";
 }
else {
  echo "Error: " . $sql . "<br>" . mysqli_error($conn);
}



}

?>
<!-- content starts -->

<div>
  <ul class="breadcrumb">
    <li>
      <a href="#">Home</a>
    </li>
    <li>
      <a href="#">Blog</a>
    </li>
  </ul>
</div>

<div class="col-md-8 offset-md-2">
  <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="POST" enctype="multipart/form-data">
   <label>Enter Title :</label>
   <input type="text" name="title" class="form-control" placeholder="Enter Title..."><br />
   <label>Choose Catagory :</label>
   <span class="checkbox-inline"><p><input type="checkbox" name="cat[]" value="Com" /> C</p></span>
   <span class="checkbox-inline"><p><input type="checkbox" name="cat[]" value="besi" /> C++</p></span>
   <span class="checkbox-inline"><p><input type="checkbox" name="cat[]" value="valo" /> C#</p></span>
   <span class="checkbox-inline"><p><input type="checkbox" name="cat[]" value="kalo" /> Java</p></span>
   <span class="checkbox-inline"><p><input type="checkbox" name="cat[]" value="sada" /> PHP</p></span> <br /><br />

   <label>Add Tags :</label>
   <span class="checkbox-inline"><p><input type="checkbox" name="tag[]" value="C" /> C</p></span>
   <span class="checkbox-inline"><p><input type="checkbox" name="tag[]" value="C++" /> C++</p></span>
   <span class="checkbox-inline"><p><input type="checkbox" name="tag[]" value="C#" /> C#</p></span>
   <span class="checkbox-inline"><p><input type="checkbox" name="tag[]" value="Java" /> Java</p></span>
   <span class="checkbox-inline"><p><input type="checkbox" name="tag[]" value="PHP" /> PHP</p></span> <br /><br />
   <label>Enter Content:</label>
   <textarea class="ckeditor from-control" name="editor1"></textarea><br />

   <label>Card Image</label>
   <input type="file" name="image" alt="image"><br />
   <input type="submit" name="submit" class="btn btn-lg btn-primary" value="Submit"><br /><br />
 </form>
</div>
<?php } ?>

<?php include"inc/footer.php";?>