Invalid query: Out of sort memory, consider increasing server sort buffer size select group_concat(tags.id separator ',') as tags_ids, faq.* from tags_x_faq left outer join faq on faq.id = tags_x_faq.id_faq left outer join tags on tags.id = tags_x_faq.id_tag where online like 'Yes' and id_faq in ( select id_faq from tags_x_faq WHERE id_tag=31 ) group by faq.id