Can't insert with sql the date which i picked from calendar - php

Question

I am trying to do a project from university and I can't figure out how to insert the date which I pick from calendar function. I have tried a couple of things, but I get 0000-00-00 or the current date: 2014-06-08.
<?php
$con=mysqli_connect("","","","");
// Check connection
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
// escape variables for security
$checkin = mysqli_real_escape_string($con, $_POST['checkin']);
$checkout = mysqli_real_escape_string($con, $_POST['checkout']);
$firstname = mysqli_real_escape_string($con, $_POST['firstname']);
$lastname = mysqli_real_escape_string($con, $_POST['lastname']);
$title = mysqli_real_escape_string($con, $_POST['title']);
$roomtype = mysqli_real_escape_string($con, $_POST['roomtype']);
$email = mysqli_real_escape_string($con, $_POST['email']);
$phone = mysqli_real_escape_string($con, $_POST['phone']);
$checkout = date("Y-m-d");
$sql="INSERT INTO reservation (checkin, checkout, firstname, lastname, title, roomtype, email, phone)
VALUES ('$checkin', '$checkout', '$firstname','$lastname', '$title', '$roomtype', '$email', '$phone')";
if (!mysqli_query($con,$sql)) {
die('Error: ' . mysqli_error($con));
}
echo "Your booking has been completed";
mysqli_close($con);
header("Location: ");
exit;
?>

Answer 1

$checkout = date("Y-m-d");
The function give you the current date in the format "Y-m-d" That is the first reason why you get the current date and because you save the current date after you did : $checkout = mysqli_real_escape_string($con, $_POST['checkout']); you override the date you get with $_POST['checkout']
You should do this:
$checkout = mysqli_real_escape_string($con, $_POST['checkout']);
$checkout = date_format(date_create($checkout), 'Y-m-d');

Answer 2

The problem is probably with your html form. HTML5 allows for an easy date picker:
<input type="date" name="checkin">
<input type="date" name="checkout">
You dont need value="DD/MM/YY" and onfocus and those other arguments. If a date input is left empty it will return nothing. The input also outputs the date as a unix timestamp I believe