outputting fields in a CSV

I am trying to loop through the fields in my database using the following code but nothing is being output [php] $fp = fopen(realpath(‘./’) .’/’. file_directory_path() .’/auto-csv/’. $filename, ‘w+’);       $data = db_result(db_query(“SELECT * FROM {actionmedicalresearch_gdpr_optin}”));       foreach ($data as $fields)[…]