一个案例彻底弄懂如何正确使用mysql inndb联合索引

有一个业务是查询最新审核的5条数据

SELECT `id`, `title`
FROM `th_content`
WHERE `audit_time` < 1541984478
 AND `status` = 'ONLINE'
ORDER BY `audit_time` DESC, `id` DESC
LIMIT 5;