Checkbox item which has been checked needs to get added to php mysql database

I have many checkbox items where each employee has access to different department . I want to add checked items into database.

code to display access to doors if checked

 $door1 = $_POST['door1'];
 echo ' dooraccess is available for ' .$door1. '<br>'; 

 $door2 = $_POST['door2'];
 echo 'dooraccess is available for  ' .$door2. '<br>'; 

 $door3 = $_POST['door3'];
 echo 'dooraccess is available for  ' .$door3. '<br>'; 

 $door4 = $_POST['door4'];
 echo 'dooraccess is available for  ' .$door4. '<br>'; 

 $door5 = $_POST['door5'];
 echo 'dooraccess is available for  ' .$door5. '<br>'; 

 $door6 = $_POST['door6'];
 echo 'dooraccess is available for  ' .$door6. '<br>'; 

 $door7 = $_POST['door7'];
 echo 'dooraccess is available for  ' .$door7. '<br>'; 

 $door8 = $_POST['door8'];
 echo 'dooraccess is available for  ' .$door8. '<br>'; 

 $door9 = $_POST['door9'];
 echo 'dooraccess is available for  ' .$door9. '<br>'; 

 $door10 = $_POST['door10'];
 echo 'dooraccess is available for  ' .$door10. '<br>'; 

 $door11 = $_POST['door11'];
 echo 'dooraccess is available for  ' .$door11. '<br>'; 

 $door12 = $_POST['door12'];
 echo 'dooraccess is available for  ' .$door12. '<br>'; 

In case the values that was not checked then it will display the error as below:

Undefined index: door7 in [since door7 was not checked]

Code to insert these values along with other values to database php mysql database

 if(isset($_POST['submit']))
  { 
   $query = "INSERT INTO form_details1(firstname,secondname,location,designation,fileno,doa,doj,cardtype1,cardcolor,cardtype2,door1,door2,door3,door4,door5,door6,door7,door8,door9,door10,door11,door12,door13) VALUES('$firstname','$secondname','$location','$designation','$fileno','$doa','$doj','$cardtype1',$cardcolor,'$cardtype2','$door1','$door2','$door3','$door4','$door5','$door6','$door7','$door8','$door9','$door10','$door11','$door12')"; //query
  if(mysqli_query($connect,$query)){ //check query executed or not
     echo 'inserted' . '<br>' ;
   }

Query doesn't insert into database since query has the values which is unchecked

I want to check all the checked items using if loop or any other means and enter only those items that has been checked. How can I do this ?