Du burde bare kunne erstatte keyword_ids med den kolonne, du ønsker at samle.http://www.experts-exchange.com/questions/20955939/Mysql-group-concat-alternative-in-3-23-x.html
SELECT @prev_item_id := NULL;
SELECT MAX(@keyword_ids := IF(@prev_item_id = item_id, CONCAT_WS(',',
@keyword_ids, keyword_ids), keyword_ids)),
@prev_item_id := item_id
FROM mytable
GROUP BY item_id;