echo json_encode(R::getAll('SELECT * FROM `category` WHERE `id_user` = 100'));$id_user = 100;
echo json_encode(R::getAll('SELECT * FROM `category` WHERE `id_user` = $id_user')); "SELECT * FROM `category` WHERE `id_user` = $id_user"'SELECT * FROM `category` WHERE `id_user` = ' . $id_user