How to insert data into two relational tables?

Table 1: product _category with sample records

Table 2: product with sample records

SQL for the above tables.

File name: my_db.sql

DROP DATABASE IF EXISTS `sms`;

DROP DATABASE IF EXISTS `sms`;

create database sms;

use sms;
DROP TABLE IF EXISTS `product_category`;

CREATE TABLE `product_category`(
  `id` int(10) unsigned NOT NULL primary key auto_increment,
  `name` varchar(50)  default NULL
 ) ENGINE=MyISAM;
DROP TABLE IF EXISTS `product`;
CREATE TABLE`product`(
  `id` int(10) unsigned NOT NULL primary key auto_increment,
  `name` varchar(50)  default NULL,
  `price` int(10)  default NULL,
  `category_id` int(10)  default NULL
 ) ENGINE=MyISAM;

Interface Design:

HTML code for above user interface

File name: demo.htm

<form action="save.php" method="post">
<table>
	<tr>
    	<td>Name</td>
        <td><input type="text" name="txtName" /></td>
    </tr>
    <tr>
    	<td>Price</td>
        <td><input type="text" name="txtPrice" /></td>
    </tr>
    <tr>
    	<td>Category</td>
        <td><input type="text" name="txtCategory" /></td>
    </tr>
    <tr>
    	<td></td>
        <td><input type="submit" value="Submit" name="btnSubmit"/></td>
    </tr>
</table>
</form>

PHP Code:

File name: save.php

<?php 
		if (isset($_POST["btnSubmit"])){
		$name=$_POST["txtName"];
		$price=$_POST["txtPrice"];
		$category=$_POST["txtCategory"];
		
	$db=new mysqli("localhost","root","****","Your DB");
	$db->query("insert into product_category(name)values('$category')");
	$last_id=$db->insert_id;
	$db->query("insert into product(name,price,category_id)values('$name','$price','$last_id')");
	}
?>