I hope this one is not a duplicate :-)
SELECT `term`.`oid`, `term`.`url`, `term`.`uid` FROM `term`
STRAIGHT_JOIN `thread` ON `thread`.`iid` = `term`.`oid` AND `thread`.`uid` = `term`.`uid`
WHERE `term`.`type` = 7 AND `term`.`term` > '2017-04-01 21:40:03' AND `thread`.`mention`
GROUP BY `term`.`url`, `term`.`uid` ORDER BY `term`.`term` DESC;
Gives
ERROR 1055 (42000): Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'friendica.term.oid' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
Most helpful comment
Fixed in https://github.com/friendica/friendica/pull/3323