SELECT `object_id` FROM `gncdso4xk_term_relationships` WHERE `term_taxonomy_id` IN (SELECT `term_taxonomy_id` FROM `gncdso4xk_term_taxonomy` WHERE `term_id` IN (SELECT `term_id` FROM `gncdso4xk_terms` WHERE `name` = '??????'))
Так выберутся ид постов, связанных с термом с именем «??????».
Можно добавить название таксономии в запрос:
SELECT `object_id` FROM `gncdso4xk_term_relationships` WHERE `term_taxonomy_id` IN (SELECT `term_taxonomy_id` FROM `gncdso4xk_term_taxonomy` WHERE `taxonomy` = 'taxonomy-name' AND `term_id` IN (SELECT `term_id` FROM `gncdso4xk_terms` WHERE `name` = '??????'))