一个查询既有order by desc 又有LIMIT下的排序如何建立索引

一个查询既有order by desc 又有LIMIT下的排序如何建立索引
一个查询既有order by desc 又有limit 的如何建立索引
一个表a没有建立索引也没主键.
select * from (select * from a where id ='12345' order by date desc limit 10) a order by date;
请问这句怎么建索引,嗯表a差不多100万行
select * from (select * from a where id ='12345' order by date desc limit 30) a order by date; ----- a差不多100万行,为innodb类型
且id 不唯一；建立复合键时,外层的select 不走索引.我想要的是外层也走索引的建议,