sql求优化

ljc

select * from
(select *,(@i:= @i+1) AS r from nl_group g,(select @i:=0) b order by end_time desc) a
        where r>(select r from
     (select *,(@i:= @i+1) AS r from nl_group g,(select @i:=0) b  order by end_time desc) a  
     where gid=1)

以上的sql已经达到我想要的，但是感觉写的好复杂，那个a不能在里面复用么