select * from (select @n:=@n+1 as n, a.* from (select * from tablename order by id desc)a,(select @n:=0)b)c where c.n%2=1 limit 10
首先 ：select @n:=@n+1 as n, a.* from (select * from tablename order by id desc)a,(select @n:=0)b 是给每行的记录添加了序号，字段名为n。
其次：where c.n%2=1 是对2取模值也就是取余数，2代表着隔一行取一条数据，如果是隔两行取一条数据，就是where c.n%3=1，以此类推。
最后：limit 10 是限制条数为10条。