Try something like this.  This function accurately inserts into my database and also scrapes for SQL injection.  
function addRestaurant() {
    if(isset($_POST['submit'])) {
        global $connection;
        $name = $_POST['name'];
        $address = $_POST['address'];
        $city = $_POST['city'];
        $state = $_POST['state'];       
        $zipcode = $_POST['zipcode'];
        $googlemapslink = $_POST['googlemapslink'];
        $restauranttype = $_POST['restauranttype'];
        $website = $_POST['website'];
        $logo = $_POST['logo'];
        $sitelink = $_POST['sitelink'];
        if ($googlemapslink == "") {
            $googlemapslink = "https://youtu.be/dQw4w9WgXcQ";
        }
        if ($website == "") {
            $website = "https://youtu.be/dQw4w9WgXcQ";
        }
        if ($logo == "") {
            $logo = "https://youtu.be/dQw4w9WgXcQ";
        }
        $name = mysqli_real_escape_string($connection, $name);
        $address = mysqli_real_escape_string($connection, $address);
        $city = mysqli_real_escape_string($connection, $city);
        $state = mysqli_real_escape_string($connection, $state);
        $zipcode = mysqli_real_escape_string($connection, $zipcode);
        $googlemapslink = mysqli_real_escape_string($connection, $googlemapslink);
        $restauranttype = mysqli_real_escape_string($connection, $restauranttype);
        $website = mysqli_real_escape_string($connection, $website);
        $logo = mysqli_real_escape_string($connection, $logo);
        $sitelink = mysqli_real_escape_string($connection, $sitelink);
        $query = "INSERT INTO `restaurants` (Name, Address, City, State, ZipCode, GoogleMapsLink, Website, RestaurantType, RestaurantLogo, SiteLink) ";
        $query .= "VALUES (";
        $query .= "'$name', ";
        $query .= "'$address', ";
        $query .= "'$city', ";
        $query .= "'$state', ";
        $query .= "'$zipcode', ";
        $query .= "'$googlemapslink', ";    
        $query .= "'$website', ";
        $query .= "'$restauranttype', ";
        $query .= "'$logo', ";
        $query .= "'$sitelink'); ";
        $filesite = "restaurants/" . $sitelink;
        $file = "restaurants/menu.php";
        $contents = file_get_contents($file);
        file_put_contents($filesite, $contents);
        $result = mysqli_query($connection, $query);
            if(!$result) {
                die("Query failed." . mysqli_error($connection));
            } else {
                echo "Record updated!";
            }
    }
}