SQL 分組後獲取每組中最大值

場景：sql server 2008

 1 drop table ID
 2 CREATE TABLE ID  
 3 (  
 4 id int identity(1,1)  not null,
 5 code int ,
 6 D date,
 7  PRIMARY KEY  (id)
 8 )  
 9 
10 insert into ID(code,D) values(0001,getdate())  
11 insert into ID(code,D) values(0002,getdate()) 
12 insert into ID(code,D) values(0002,getdate()) 
13 insert into ID(code,D) values(0003,getdate()) 
14 insert into ID(code,D) values(0003,'2017-08-02') 
15 insert into ID(code,D) values(0003,'2017-08-01') 
16 
17 select * from ID

目標：

select COUNT(*) from ID group by code

產生code列惟一的3行數據，並顯示最小的D列數據

 

方案1：

select code,MIN(D)
from ID group by code

方案2：

是否有重複code行

select COUNT(*) from ID where
code in(select code from ID group by code having COUNT(*) > 1)

@1

select * into #a from ID
delete from #a
where code in (select code from #a group by code having count(code) > 1)
and D not in (select min(D) from #a group by code having count(code) > 1)
select * from #a

刪掉記錄數最多的中一條數據

反覆執行

方案3：

select code,D from( select MIN(D) from ID where COUNT(code)>1)t1 right join ID t2 on t1.D=t2.D