场景：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
目标：
select COUNT(*) from ID group by code
产生code列唯一的3行数据，并显示最小的D列数据
方案1：
select code,MIN(D)
from ID group by code
方案2：
是否有重复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
删掉记录数最多的中一条数据
反复执行
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