An Error Was Encountered

Error Number: 1055

Expression #6 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'sel.foto_name' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

SELECT *, GROUP_CONCAT(DISTINCT tag) AS tags FROM ( SELECT t.num, t.titulo, t.spare_1, t.texto,, i.foto_name, i.titulo AS filename, i.caption , tt.tag FROM site_content_txt AS t LEFT JOIN site_images AS i ON t.num = i.gal_id LEFT JOIN site_content_to_tags AS ct ON t.num = ct.post_id LEFT JOIN site_tags AS tt ON ct.tag_id = tt.tag_id WHERE t.num = '49' AND = 'yes' ORDER BY i.position ASC ) AS sel GROUP BY num LIMIT 1