An Error Was Encountered

Error Number: 1055

Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'tkf.treeAssign.cmsTreeId' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

SELECT DISTINCT `treeAssign`.`cmsTreeId`, `pageUrls`.`url` FROM `treeAssign` LEFT JOIN `articles` ON `treeAssign`.`moduleId` = `articles`.`id` LEFT JOIN `pageUrls` ON `pageUrls`.`uid` = `articles`.`id` AND `pageUrls`.`tabela` = 'articles' WHERE `treeAssign`.`module` = 'articles' AND `treeAssign`.`lang` = 'pl' GROUP BY `articles`.`id`