Warning:  [mysql error 3065] Expression #1 of ORDER BY clause is not in SELECT list, references column 'lwoacomi_piwi1.piwi_images.file' which is not in SELECT list; this is incompatible with DISTINCT

SELECT DISTINCT(image_id)
  FROM piwi_image_category
    INNER JOIN piwi_images ON id = image_id
  WHERE
    category_id = 7

  ORDER BY file ASC
; in /home/lwoacomi/public_html/gallery/include/dblayer/functions_mysqli.inc.php on line 830