<?php

$servername = "localhost";
$username = "root";
$password = "";
$dbname = "camping";


// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}
// Start date
$date = '2017-01-04';
// End date
$end_date = '2017-01-14';

while (strtotime($date) <= strtotime($end_date)) {
       $sql = "INSERT INTO `availability` (`id`, `date`, `available`, `accommodation_id`) VALUES (NULL, '$date', '1', 1)";
                $date = date ("Y-m-d", strtotime("+1 day", strtotime($date)));
}

if ($conn->query($sql) === TRUE) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}
?>