how to call json with and without data [on hold]

i tried to make a json from php and want it can be get with data like http://localhost/moviereview/?action=get_review&genre=biography and or without data like http://localhost/moviereview/?action=get_review

this is the code that i tried

 $query = mysqli_query($connection, 'SELECT user_review.*, data_movie.* FROM data_movie INNER JOIN user_review ON data_movie.id = user_review.id_movie WHERE genre = "'. $genre .'" order by created_at desc')
  or mysqli_query($connection, 'SELECT user_review.*, data_movie.* FROM data_movie INNER JOIN user_review ON data_movie.id = user_review.id_movie order by created_at desc')
  or die(mysqli_error($connection));

but it doesn't work. please help