要求：获得按table1_id分组，并且age最大的记录信息，即2、3、5条

 

 

方法一：

select * from (select * from table2 order by age desc) as a group by a.table1_id

 

方法二：

select a.* from table2 as a where age = (select max(age) from table2 where a.table1_id=table1_id)

 

方法三：

select a.* from table2 as a where not exists (select * from table2 where table1_id=a.table1_id and age>a.age)

 

方法四：

select a.* from table2 as a where exists (select count(*) from table2 where table1_id=a.table1_id and age>a.age having count(*)=0)