Thank you for your answer ggppdk,
Here are the queries :
SELECT SQL_CALC_FOUND_ROWS DISTINCT i.id FROM #__flexicontent_items_tmp AS i JOIN #__flexicontent_types AS ty ON i.type_id = ty.id JOIN #__flexicontent_cats_item_relations AS rel ON rel.itemid = i.id JOIN #__categories AS c ON c.id = i.catid LEFT JOIN #__flexicontent_fields_item_relations AS f ON f.item_id = i.id AND f.field_id=16 LEFT JOIN #__flexicontent_fields_item_relations AS f2 ON f2.item_id = i.id AND f2.field_id=16 WHERE 1 AND rel.catid IN ('114', '115', '116', '117', '118', '119', '271') AND ty.access IN (0,1,1,2,3,6,9,10) AND c.access IN (0,1,1,2,3,6,9,10) AND i.access IN (0,1,1,2,3,6,9,10) ORDER BY ISNULL(f.value), f.value ASC, ISNULL(f2.value), f2.value ASC, i.title
SELECT i.*, ie.*, u.name as author, ty.name AS typename, ty.alias AS typealias, rel.catid as rel_catid, c.title AS maincat_title, c.alias AS maincat_alias, CASE WHEN CHAR_LENGTH(i.alias) THEN CONCAT_WS(':', i.id, i.alias) ELSE i.id END as slug, CASE WHEN CHAR_LENGTH(c.alias) THEN CONCAT_WS(':', c.id, c.alias) ELSE c.id END as categoryslug, c.access as category_access, ty.access as type_access, 1 AS has_access FROM #__content AS i JOIN #__flexicontent_items_ext AS ie ON ie.item_id = i.id JOIN #__flexicontent_types AS ty ON ie.type_id = ty.id JOIN #__flexicontent_cats_item_relations AS rel ON rel.itemid = i.id JOIN #__categories AS c ON c.id = i.catid LEFT JOIN #__users AS u ON u.id = i.created_by WHERE i.id IN (8232,9254,5649,8863,8233,7924,8557,7455,8231,104,8867,8520,7457,7312,8252,5629,9255,7306,8167) GROUP BY i.id