Store checkbox value in database

Question

Below is code that I am using, when i submit the survey, arrrive and mode work but not trans/checkboxes, data comes back displayed as 'on' in table (survey) database (wdtlabwork), also the field is trans, same with the other two being mode n arrive in the database, all fields were type VARCHAR. Apologies if formatting is bad i am new to site. NOTE: I want the data to come back as either car, train or bus but because its checkboxes if the user checked train and car i want the database to display train and car.

HTML

<section id="content">
<form action="connect.php" method="post">
<div class="col-6 col-s-9">
  <h3>Available Transportation?</h3>
<input id="trans1" type="checkbox" name="trans[]"><label for ="trans1">Car</label>
<input id="trans2" type="checkbox" name="trans[]"><label for ="trans2">Train</label>
<input id="trans3" type="checkbox" name="trans[]"><label for ="trans3">Bus</label>
<h4>How do you intend to arrive at the Hostel?</h4>
<input id="arrive1" type="radio" value="car" name="arrive"><label for="arrive1">Car</label>
<input id="arrive2" type="radio" value="train" name="arrive"><label for="arrive2">Train</label>
<input id="arrive3" type="radio" value="bus" name="arrive"><label for="arrive3">Bus</label>
<h5>Preferred mode of transport?</h5>
<select name="mode">
<option selected hidden value="">Select Option</option>
<option value="car">Car</option>
<option value="train">Train</option>
<option value="bus">Bus</option>

</select><input type="submit" class="btn btn=primary"></div></section>

PHP

<?php
$arrive = $_POST['arrive'];
$trans = $_POST['trans'];
$mode = $_POST['mode'];

$conn = new mysqli('localhost', 'root','','wdtlabwork');


if ($conn->connect_error){
    die('Connection Failed : '.$conn-> connect_error);
}else{
$stmt = $conn->prepare("insert into survey(trans, arrive, mode)
    values(?, ?, ?)");
$stmt->bind_param("sss",$trans, $arrive, $mode);
$stmt->execute();
echo "registration successfully...";
$stmt->close();
$conn->close();
}

?>

Answer 1

Your input fields do not have value= attribute so they default to on as described here: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/checkbox#Value

To get the values in the POST you need to specify the values, for example:

<input id="trans1" type="checkbox" name="trans[]" value ="car"><label for ="trans1">Car</label>
<input id="trans2" type="checkbox" name="trans[]" value ="train"><label for ="trans2">Train</label>
<input id="trans3" type="checkbox" name="trans[]" value ="bus"><label for ="trans3">Bus</label>

Then in your PHP you would receive an array of the selected elements in $_POST['trans'] . If you would like to join them ( not recommended ) to be saved in a single field in the database you can just use implode(',', $_POST['trans']) , for example:

$trans = implode(',', $_POST['trans']);
$arrive = $_POST['arrive'];
$mode = $_POST['mode'];