Row is inserted into database everytime I refresh the jquery mobile page

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PHP

MySQL

jQuery

forms

I am making a jquery mobile web app and I am using a multi page layout. I connect to mySQL when the page loads and on the second div page, I have a form which using a php file sends the values in the form to mySQL database when submitted.

My problem is, when I click/tap the submit button it inserts into the database even if there is no data in the form elements and redirects to my localhost/share/add_journey.php. I'm relatively new to web app development and would like any help as to what I'm doing wrong.

Advice on how best to insert to a mySQL database through php on a multi-page layout would be great. Please let me know if I need to show more code.

<!--Top of second page within multi page layout containing form-->
<!-- The POST A JOURNEY page where user creates a journey to be seen by others-->
    <div data-role="page" id="postAJourney" data-add-back-btn="true" data-back-btn-text="back" data-rel="back" data-direction="reverse" data-transition="flip" data-theme="b" >
        <div data-role="header"  data-position="fixed">
            <h1>Post A Journey</h1>
        </div>

        <div data-role="content">
            <form action="add_journey.php" method="post" id="postAJourneyForm">

<!--Top of multipage layout-->
<?php
require 'database.php';
?>

Updated

<?php

//get the journey data
	$radUserType = intval($_POST['radUserType']);
	$pjFrom = $_POST['pjFrom'];
	$pjTo = $_POST['pjTo'];
	$radioJourneyType = intval($_POST['radioJourneyType']);
	$departDate = $_POST['departDate'];
	$returnDate = $_POST['returnDate'];
	$textareanotes = $_POST['textAreaNotes'];

//check all values from $_POST
$canSubmitForm = false;
$isFormEmpty = false;

if (empty($pjFrom) || empty($pjTo))
{
	$isFormEmpty = true;
}

//check for your data here
if(isset($radUserType) && isset($pjFrom) && isset($pjTo) && isset($radioJourneyType) && isset($departDate) && isset($returnDate) && isset($textareanotes))
{
	$canSubmitForm = true;
}

$departTime = '11:12';
$returnTime = '11:16';
$seatcounter = '2';

//will only get executed if true
if ($canSubmitForm)
{
	if ($isFormEmpty == false)
	{
	require_once('database.php');
	$query = "INSERT INTO journey
		(from_destination,to_destination,journey_type,depart_date,depart_time,return_date,return_time,seats_available,journey_message,user_type)
		VALUES('$pjFrom','$pjTo','$radioJourneyType','$departDate','$departTime','$returnDate','$returnTime','$seatcounter','$textareanotes','$radUserType')";
	$db->exec($query);
	
	include('index.php');
	}
}
else
{
	$error = "Invalid product data. Check all fields and try again.";
	include('error.php');
}
//Display the Product List page
?>