How to send a PHP request using AJAX?

Question

SQL

Hello guys, such a problem. There is a form, there is a PHP request and ajax code. Without AJAX, PHP sends data to the DB. With ajax for some reason not.

<form action="" id="ajax_form" method="POST">
  <label for="head_logo_photo" class="">Логотип </label><!---->
  <input id="head_logo_photo"  name="logo_link" type="text" placeholder="Введите название" class="form-control">
  <label for="head_adres">Адрес</label>
  <input type="text" id="head_adres"  name="adres" placeholder="Адрес" class="form-control">
  <label for="head_phone">Телефон</label>
  <input type="text" id="head_phone" name="phone" class="form-control" placeholder="Телефон">
  <label for="head_tab">Первая вкладка</label>
  <input type="text" id="head_tab" name="tab1" class="form-control" placeholder="Вкладка">
  <label for="head_tab2">Вторая вкладка</label>
  <input type="text" name="tab2" id="head_tab2" class="form-control" placeholder="Вкладка">
  <label for="head_tab3">Третья вкладка</label>
  <input type="text" id="head_tab3" name="tab3" class="form-control" placeholder="Вкладка">
  <label for="head_tab4">Четвертая вкладка</label>
  <input type="text" id="head_tab4" name="tab4" class="form-control" placeholder="Вкладка">
  <label for="" id="result"></label>
                                                 
  <div class="button-position">
    <input type="submit"  id="head_add" name="head_add" class="btn btn-success btn-block btn_struct" value="Сохранить">
    <input type="submit" name="head_delete" class="btn btn-danger btn-block btn_struct" value="Удалить">
  </div>
</form>

<?php
       require_once ("connection.php");
if (isset($_POST['head_add'])) {
     # code...

     $logo=$_POST['logo_link'];
     $adres=$_POST['adres'];
     $phone=$_POST['phone'];
     $tab1=$_POST['tab1'];
     $tab2=$_POST['tab2'];
     $tab3=$_POST['tab3'];
     $tab4=$_POST['tab4'];
     $query="INSERT INTO header (id, logo, adres, phone, tab1, tab2, tab3, tab4) VALUES (NULL,'$logo', '$adres', '$phone', '$tab1', '$tab2', '$tab3', '$tab4')";
     mysqli_query($link,$query);

 }

?>

$("document").ready(function(){
$("#head_add").click(function()
{
   event.preventDefault();
   sendAjaxForm('result','ajax_form','../PHP/header_add_delete.php');
   
  });
});
function sendAjaxForm(result,ajax_form,url){
  $.ajax({
    url: url,
    type: "POST",
    dataType: "html",
    data: $(this).serialize(),
     success: function(){
       alert("AJAX работает!");
     }
  });
}

When you click on the Save button, it displays an alert with the inscription AJAX is working. But the data is not sent to the database.

Answer 1

Select country_id from (Select unnest(country) as counrry_id from table)_ group by country_id having count(*) > 5

Answer 2

data: $(this).serialize(),
Here, presumably, the form was meant, and not the empty this of the called function.