sql查询

数据表如图:查询后的表如图:

方法一:查询后如图:语句如下:select userid,userAge,(select count(*) as t from [user] e where e.userAge=a.userAge) t from [user] a order by t desc,userAge desc

分组汇总1.select distinct username,(select  top 1 datetime from user b where a.username=b.username order by datetime ) from user a

          2.select username, max(datetime) from user group by username