求一sql算法

[Pra_lijian]

将如下规律的集合
A , B , 1
A , B , 2
A , B , 3
A , C , 1
A , C , 2
A , C , 3
A , D , 1
A , D , 2
A , D , 3
想转化成:
A, B, 1
A, C, 2
A, D, 3
sql怎么写呢?

[中国风]

select *
from
t a
where
not exists(select 1 from t where col1=a.col1 and col2=a.col2 and col3>a.col3)

[中国风]

select
col1,
col2,
min(col3)
from t
group by col1, col2

[wzy_love_sly]

select col1,col2,row_number() over(order by col2)
from tb group by col1,col2

[wzy_love_sly]

insert into @tb select 'a','c',1
insert into @tb select 'a','c',2
insert into @tb select 'a','c',3

insert into @tb select 'a','d',1
insert into @tb select 'a','d',2
insert into @tb select 'a','d',3

select col1,col2,row_number() over(order by col2)
from @tb group by col1,col2

col1 col2 (无列名)
a b 1
a c 2
a d 3

[中国风]

--col2有大小关系时
select
	distinct
	col1,
	col2,
	col3=(select count(1) from T where col1=a.col1 and col2!>a.col2)
from 
	T a

[dawugui]

将如下规律的集合
A , B , 1
A , B , 2
A , B , 3
A , C , 1
A , C , 2
A , C , 3
A , D , 1
A , D , 2
A , D , 3
想转化成:
A, B, 1
A, C, 2
A, D, 3
sql怎么写呢?

--2000
select distinct col1,col2, col3 = identity(int,1,1) into tmp from tb
select * from tmp

--2005
select col1 , col2 , id = rownumber() over(order by col1 , col2) from
(
  select distinct col1 , col2 from tb
) t

[中国风]

以上为2000写法，05：row_number排序
第2列col2没有大小关系时，用临时表实现效率好一点，用语句嵌套效率低

[Pra_lijian]

如上方法得到结果为:
A, B, 3
A, C, 3
A, D, 3

[中国风]

--用这个
--col2有大小关系时
select
distinct
col1,
col2,
col3=(select count(1) from T where col1=a.col1 and col2!>a.col2)
from
T a

[中国风]

用大小关系时，用生成临时表的方法..

[dawugui]

--sql server 2000的写法.
create table tb(col1 varchar(10) , col2 varchar(10), col3 varchar(10))
insert into tb values('A'   ,   'B'   ,   1 )
insert into tb values('A'   ,   'B'   ,   2 )
insert into tb values('A'   ,   'B'   ,   3 )
insert into tb values('A'   ,   'C'   ,   1 )
insert into tb values('A'   ,   'C'   ,   2 )
insert into tb values('A'   ,   'C'   ,   3 )
insert into tb values('A'   ,   'D'   ,   1 )
insert into tb values('A'   ,   'D'   ,   2 )
insert into tb values('A'   ,   'D'   ,   3 )
go

select col1,col2,id = identity(int , 1, 1) into tmp from
(
  select distinct col1,col2 from tb
) t

select * from tmp

drop table tb,tmp

/*
col1       col2       id          
---------- ---------- ----------- 
A          B          1
A          C          2
A          D          3

（所影响的行数为 3 行）
*/

[wzy_love_sly]

declare @tb table (col1 varchar(10),col2 varchar(10),col3 int)
insert into @tb select 'a','b',1
insert into @tb select 'a','b',2
insert into @tb select 'a','b',3

insert into @tb select 'a','c',1
insert into @tb select 'a','c',2
insert into @tb select 'a','c',3

insert into @tb select 'a','d',1
insert into @tb select 'a','d',2
insert into @tb select 'a','d',3

select col1 , col2 , id = row_number() over(order by col1 , col2) from
(
  select distinct col1 , col2 from @tb
) t

都行

[dawugui]

--sql server 2005的写法.
create table tb(col1 varchar(10) , col2 varchar(10), col3 varchar(10))
insert into tb values('A'   ,   'B'   ,   1 )
insert into tb values('A'   ,   'B'   ,   2 )
insert into tb values('A'   ,   'B'   ,   3 )
insert into tb values('A'   ,   'C'   ,   1 )
insert into tb values('A'   ,   'C'   ,   2 )
insert into tb values('A'   ,   'C'   ,   3 )
insert into tb values('A'   ,   'D'   ,   1 )
insert into tb values('A'   ,   'D'   ,   2 )
insert into tb values('A'   ,   'D'   ,   3 )
go

select col1,col2,id = row_number() over(order by col1 , col2) from
(
  select distinct col1,col2 from tb
) t

drop table tb

/*
col1       col2       id          
---------- ---------- ----------- 
A          B          1
A          C          2
A          D          3

（所影响的行数为 3 行）
*/

[ORARichard]

select 'A' c1   ,   'B' c2  ,   1 c3 into # union all
select 'A'   ,   'B'   ,   2 union all
select 'A'   ,   'B'   ,   3 union all 
select 'A'   ,   'C'   ,   1  union all
select 'A'   ,   'C'   ,   2  union all
select 'A'   ,   'C'   ,   3  union all
select 'A'   ,   'D'   ,   1  union all
select 'A'   ,   'D'   ,   2  union all
select 'A'   ,   'D'   ,   3 

select c1,c2,c3=(select count(0) from (select distinct c1,c2 from #) v where v.c1=t.c1 and v.c2<=t.c2)
from ( select distinct c1,c2 from #) t
drop table #

/*
c1   c2   c3
---- ---- -----------
A    B    1
A    C    2
A    D    3

(3 row(s) affected)
*/

[Pra_lijian]

当第三行不是1,2,3 而是一些无规律的数字时呢?