Warning:  [mysql error 1054] Unknown column 'com.author_id' in 'on clause'

SELECT COUNT(DISTINCT(com.id))
  FROM dg_image_category AS ic
    INNER JOIN dg_comments AS com
    ON ic.image_id = com.image_id
    LEFT JOIN dg_users As u
    ON u.id = com.author_id
  WHERE 1=1
    AND validated='true'
    AND  (category_id NOT IN (14,31) AND ic.image_id NOT IN (45,51,62,64,66,67))
; in /home/dg1/ftp/DIGITALGARDENS/galeria/include/dblayer/functions_mysql.inc.php on line 656

Warning:  [mysql error 1054] Unknown column 'com.author_id' in 'field list'

SELECT com.id AS comment_id,
       com.image_id,
       com.author,
       com.author_id,
       com.date,
       com.content,
       com.validated
  FROM dg_image_category AS ic
    INNER JOIN dg_comments AS com
    ON ic.image_id = com.image_id
    LEFT JOIN dg_users As u
    ON u.id = com.author_id
  WHERE 1=1
    AND validated='true'
    AND  (category_id NOT IN (14,31) AND ic.image_id NOT IN (45,51,62,64,66,67))
  GROUP BY comment_id,
       com.image_id,
       com.author,
       com.author_id,
       com.date,
       com.content,
       com.validated
  ORDER BY date DESC
  LIMIT 10 OFFSET 0
; in /home/dg1/ftp/DIGITALGARDENS/galeria/include/dblayer/functions_mysql.inc.php on line 656