主要按照日期獲得最新的資料；

今天記錄兩種方式，並不涉及效率等其他方面問題：

第一種， 利用GROUP BY原理：

select * from (
	select * from `authenticationrecord` order by `authenticationtime` desc
) `temp`  group by merchantrid order by `authenticationtime` desc

select * from `test` where id in(select SUBSTRING_INDEX(group_concat(id order by `date` desc),',',1) from `test` group by category_id ) order by `date` desc
 

<<<<<<<內容完<><><>

試驗指令碼（自己玩）：

create table STAFF(
	id  int,
	sname  varchar(50),
dept  varchar(50),
salary  int,
edlevel  int,
hiredate datetime
)

insert into STAFF values('1','張三','開發部','2000','3','2009-10-11');
insert into STAFF values('2','李四','開發部','2500','3','2009-10-01');
insert into STAFF values('3','王五','設計部','2600','5','2010-10-02');
insert into STAFF values('4','王六','設計部','2300','4','2010-10-03');
insert into STAFF values('5','馬七','設計部','2100','4','2010-10-06');
insert into STAFF values('6','趙八','銷售部','3000','5','2010-10-05');
insert into STAFF values('7','錢九','銷售部','3100','7','2010-10-07');
insert into STAFF values('8','孫十','銷售部','3500','7','2010-10-06');


select group_concat(id order by hiredate desc) as test from staff
group by dept;

select * from STAFF;


select * from STAFF
group by dept
 

參考網站：http://blog.csdn.net/agileclipse/article/details/12184635