查询每个人最新时间更新的数据

实现思路：inner join on + max() + group by

1. 通过合计函数max()和group by计算出每一组的最新时间；
2. 通过inner join对原表和步骤1生成进行组合，通过on条件筛选出时间最新的那条数据。

实现SQL：
SELECT * FROM personData as table1 INNER JOIN (SELECT table2.named,max(table2.date) as max FROM personData as table2 WHERE county="历下区" GROUP BY table2.named) as table3 ON table1.named = table3.name AND table1.date=table3.max

思路bug：order by + group by;