1、distinct去除重复项，s,d别名，order by s.time desc以时间逆序排列
select distinct s.time,d.area
from server.table s,device.table d
where s.id = d.id
and s.time > '2017-04-25'
order by s.time desc
2、left join,right join,inner join，左、右、内连接
select s.*,d.* from s left join d
on s.id = d.id