select case when 积分 between 0 and 500 then 一级
when 积分 between 501 and 1000 then 二级
when 积分 between 1001 and 1500 then 三级 else 无对应级别 end
from
xinxi

select t1.姓名,t1.积分,t2.会员等级
from
xinxi t1
inner join jifen t1
on t1.积分 >= t2.起始积分
and t1.积分 <= t2.结束积分