http://raozhiyong11.iteye.com/blog/1559226
SQL Server 按某一字段分组 取 最大 (小)值所在行的数据
数据如下:
name val memo
a 2 a2(a的第二个值)
a 1 a1--a的第一个值
a 3 a3:a的第三个值
b 1 b1--b的第一个值
b 3 b3:b的第三个值
b 2 b2b2b2b2
b 4 b4b4
b 5 b5b5b5b5b5
*/
-- 创建表并插入数据:
create table tb(name varchar ( 10 ),val int ,memo varchar ( 20 ))
insert intotb values ( ' a ' , 2, 'a2(a的第二个值) ' )
insert intotb values ( ' a ' , 1, 'a1--a的第一个值 ' )
insert intotb values ( ' a ' , 3, 'a3:a的第三个值 ' )
insert intotb values ( ' b ' , 1, 'b1--b的第一个值 ' )
insert intotb values ( ' b ' , 3, 'b3:b的第三个值 ' )
insert intotb values ( ' b ' , 2, 'b2b2b2b2 ' )
insert intotb values ( ' b ' , 4, 'b4b4 ' )
insert intotb values ( ' b ' , 5, 'b5b5b5b5b5 ' )
go
-- 一、按name分组 取 val最大 的值所在行的数据。
-- 方法1:
select a. * from tba where val = ( select max (val) from tb where name = a.name) order by a.name
-- 方法2:
select a. * from tba where notexists ( select 1 from tb where name = a.name and val > a.val)
-- 方法3:
select a. * from tba,( select name,max (val) val from tb group by name) b where a.name = b.name and a.val = b.val order by a.name
-- 方法4:
select a. * from tba inner join( select name , max (val) val from tb group by name) b on a.name = b.name and a.val = b.val order by a.name
-- 方法5
select a.* from tb a where 1 > ( select count ( * ) from tb where name = a.name and val > a.val ) order by a.name
/*
name val memo
---------- ----------- --------------------
a 3 a3:a的第三个值
b 5 b5b5b5b5b5
*/
-- 二、按name分组 取 val最小的值所在行的数据。
-- 方法1:
select a. * from tba where val = ( select min (val) from tb where name = a.name) order by a.name
-- 方法2:
select a. * from tba where notexists ( select 1 from tb where name = a.name and val < a.val)
-- 方法3:
select a. * from tba,( select name,min (val) val from tb group by name) b where a.name = b.name and a.val = b.val order by a.name
-- 方法4:
select a. * from tba inner join( select name , min (val) val from tb group by name) b on a.name = b.name and a.val = b.val order by a.name
-- 方法5
select a.* from tb a where 1 > ( select count ( * ) from tb where name = a.name and val < a.val) order by a.name
/*
name val memo
---------- ----------- --------------------
a 1 a1--a的第一个值
b 1 b1--b的第一个值
*/
-- 三、按name分组 取 第一次出现的行所在的数据。
select a. * from tba where val = ( select top 1 val from tb where name = a.name) order by a.name
/*
name val memo
---------- ----------- --------------------
a 2 a2(a的第二个值)
b 1 b1--b的第一个值
*/
-- 四、按name分组 随机取一条数据。
select a. * from tba where val = ( select top 1 val from tb where name = a.name order by newid ()) order by a.name
/*
name val memo
---------- ----------- --------------------
a 1 a1--a的第一个值
b 5 b5b5b5b5b5
*/
-- 五、按name分组 取 最小的两个(N个)val
select a.* from tb a where 2 > ( select count ( * ) from tb where name = a.name and val < a.val ) order by a.name,a.val
select a.* from tb a where val in ( select top 2 val from tb where name = a.name order by val) order by a.name,a.val
select a.* from tb a where exists ( select count ( * ) from tb where name = a.name and val < a.val having Count ( * ) < 2 ) order by a.name
/*
name val memo
---------- ----------- --------------------
a 1 a1--a的第一个值
a 2 a2(a的第二个值)
b 1 b1--b的第一个值
b 2 b2b2b2b2
*/
--六、按name分组取最大的两个(N个)val
select a.* from tb a where 2 > (select count(*) from tb where name = a.name and val > a.val ) order bya.name,a.val
--提取出每行的 name 和val 去数据库中找比自己小的个数。如果小于2个,代表自己就是满足条件的
select a.* from tb a where val in (select top 2 val from tb where name=a.name order by val desc) order bya.name,a.val
详细说下这个方法
select a.* fromtb a where val in --1段
(select top 2 val from tb where name=a.name order by val) --2段
order by a.name,a.val --3段
思路 先看2段。里面是按每个名称排序,然后选重最小的val的值
然后1段是从tb表里面 选出符合val值的记录
3段 是把提出出来的数据排下序
开始担心 之限制val会会出现 其他name的值也有相同的情况,然后提起的不是很准确
类似于
select a.* from tb a where val in (1,2,4,3)
开始认为是和这个类似,如果要是和这个类似的话,结果确实不对。
后来仔细思考后 得到结果,当2段里面 提取val的时候已经限制了名字,也就是说
当name为一个值的时候,只会出项和他对应的2个最小val
select a.* from tb a where exists (select count(*) from tb where name = a.name and val > a.val having Count(*)< 2) order by a.name
/*
name val memo
---------- ----------- --------------------
a 2 a2(a的第二个值)
a 3 a3:a的第三个值
b 4 b4b4
b 5 b5b5b5b5b5
*/
--七,如果整行数据有重复,所有的列都相同。
/*
数据如下:
name val memo
a 2 a2(a的第二个值)
a 1 a1--a的第一个值
a 1 a1--a的第一个值
a 3 a3:a的第三个值
a 3 a3:a的第三个值
b 1 b1--b的第一个值
b 3 b3:b的第三个值
b 2 b2b2b2b2
b 4 b4b4
b 5 b5b5b5b5b5
*/
--在sql server 2000中只能用一个临时表来解决,生成一个自增列,先对val取最大或最小,然后再通过自增列来取数据。
--创建表并插入数据:
create table tb(name varchar(10),val int,memo varchar(20))
insert into tb values('a', 2, 'a2(a的第二个值)')
insert into tb values('a', 1, 'a1--a的第一个值')
insert into tb values('a', 1, 'a1--a的第一个值')
insert into tb values('a', 3, 'a3:a的第三个值')
insert into tb values('a', 3, 'a3:a的第三个值')
insert into tb values('b', 1, 'b1--b的第一个值')
insert into tb values('b', 3, 'b3:b的第三个值')
insert into tb values('b', 2, 'b2b2b2b2')
insert into tb values('b', 4, 'b4b4')
insert into tb values('b', 5, 'b5b5b5b5b5')
go
select * , px = identity(int,1,1) into tmp from tb
select m.name,m.val,m.memo from
(
select t.* from tmp t where val = (select min(val) from tmp where name = t.name)
) m where px = (select min(px) from
(
select t.* from tmp t where val = (select min(val) from tmp where name = t.name)
) n where n.name = m.name)
drop table tb,tmp
/*
name val memo
---------- ----------- --------------------
a 1 a1--a的第一个值
b 1 b1--b的第一个值
(2 行受影响)
*/
--在sql server 2005中可以使用row_number函数,不需要使用临时表。
--创建表并插入数据:
create table tb(name varchar(10),val int,memo varchar(20))
insert into tb values('a', 2, 'a2(a的第二个值)')
insert into tb values('a', 1, 'a1--a的第一个值')
insert into tb values('a', 1, 'a1--a的第一个值')
insert into tb values('a', 3, 'a3:a的第三个值')
insert into tb values('a', 3, 'a3:a的第三个值')
insert into tb values('b', 1, 'b1--b的第一个值')
insert into tb values('b', 3, 'b3:b的第三个值')
insert into tb values('b', 2, 'b2b2b2b2')
insert into tb values('b', 4, 'b4b4')
insert into tb values('b', 5, 'b5b5b5b5b5')
go
select m.name,m.val,m.memo from
(
select * , px = row_number() over(order by name ,val) from tb
) m where px = (select min(px) from
(
select * , px = row_number() over(order by name ,val) from tb
) n where n.name = m.name)
drop table tb
/*
name val memo
---------- ----------- --------------------
a 1 a1--a的第一个值
b 1 b1--b的第一个值
(2 行受影响)
*/
我们首先再来确认一下我们要做什么事情. 只有在清楚我们需要做什么事情的情况下, 我们才能得到正确的结论. 我们要根据某一个字段(例如: name), 进行分组, 并在分组的基础上, 选出某列(例如: val)上的最值. 并最终返回name, val值在表tb中所有字段信息.
由于表tb上没有主键, 因此name, val, memo这个三元组, 不一定能从表tb中返回唯一的元组. 由于我们要根据name进行分组, 并选出val上的最值, 我们可以发现name, val的二元组, 也不一定从表tb中返回唯一的元组.
根据"爱新觉罗.毓华"设计的用例(testcase)来看, 并没有考虑当name, val相同时, memo不同时应该返回何种结果. 通过"爱新觉罗.毓华"给出的求解方案, 我们知道无论memo为何值, 利用临时表或row_number都只返回"第一个"元组.
我们已经确认了"爱新觉罗.毓华"这位朋友的文章中第七种问题的情况, 我们除了要完成"爱新觉罗.毓华"已经完成的操作(问题1). 还要实现一个能够对不同memo返回多条结果的SQL语句(问题2). 实际上问题2比问题1要容易得多.
针对问题1来说, "爱新觉罗.毓华"给出2种方法分别利用:
1. 临时表+自增列;
2. row_number函数;
我们是否还能给出第三种方法呢? 在继续讨论问题1之前, 我们先来解决问题2, 问题2更加简单. 我们首先追加一些数据:
我们只对a, b加上两条数据, 来补充一下测试用例(我们不再讨论NULL值问题).
我们首先根据name字段进行分组, 并取出val中最小值:
输出结果:
name minval
---------- -----------
a 1
b 1
(2 row(s) affected)
接下来, 我们只需要利用 "相关子查询" 或者 "JOIN" 来选出最小值对应的元组:
输出结果:
name val memo
---------- ----------- ----------------------------------------
a 1 a1--a的第一个值
a 1 问题2 ADD BY Edengundam
b 1 b1--b的第一个值
b 1 问题2 ADD BY Edengundam
(4 row(s) affected)
注意, 这里的DISTINCT用来将重复的a, 1, 'a1--a的第一个值'列消去. 现在我们已经完成了问题2, 下面我们需要思考如何能够不依赖临时表和row_number这类函数来针对不同的name, MIN(val)返回一条元组.
我们应该从tb表中选择出name, MIN(val)的列, 并且这一列的memo是通过TOP语句唯一选择的. 这就是我们的思路, 利用相关子查询, TOP语句:
我们看看输出结果:
name val memo
---------- ----------- ----------------------------------------
a 1 a1--a的第一个值
b 1 b1--b的第一个值
(2 row(s) affected)
我们已经完成任务了, 但是我必须提醒大家效率上来说, 最好的是"爱新觉罗.毓华"利用row_number函数实现的办法. 我的讨论只是帮助大家开头思路, 并且将原有讨论情况进行扩充.
本文转载于:http://hi.baidu.com/lr02/blog/item/d9262e300683ac95a9018eb7.html
问题2:
常用的文章系统,如何用一条sql语句提取出每个分类的第一条并按OrderCol字段排序。分类大概几十个,一共只要取top 10 这样
http://topic.csdn.net/u/20080122/17/8820a852-b106-4096-be23-3878e1bf825d.html?1753015752
方法1:
--取小
select top 10 t.* from tb t where OrderCol = (select min(OrderCol) from tb where 分类 = t.分类) order by OrderCol
--取大
select top 10 t.* from tb t where OrderCol = (select max(OrderCol) from tb where 分类 = t.分类) order by OrderCol desc
方法2:
select * from 文章表 a
where not exists(select 1 from 文章表 where 类别=a.类别 and OrderCol>a.OrderCol)
order byOrderCol desc
含有重复值:
--取小
select top 10 m.* from
(
select t.* from tb t whereOrderCol = (select min(OrderCol) from tb where 分类 = t.分类)
) m where id = (select min(id) from
(
select t.* from tb t whereOrderCol = (select min(OrderCol) from tb where 分类 = t.分类)
) n where m.分类 = n.分类
)
--取大
select top 10 m.* from
(
select t.* from tb t whereOrderCol = (select max(OrderCol) from tb where 分类 = t.分类)
) m where id = (select max(id) from
(
select t.* from tb t where OrderCol= (select max(OrderCol) from tb where 分类 = t.分类)
) n where m.分类 = n.分类
)
方法3:
[code=SQL]declare @t table(type varchar(4),detail varchar(10))
insert @t select
'001','a' union select
'001','sss' union select
'001','gssfa' union select
'002','fdsf' union select
'002','fs' union select
'002','gahas' union select
'003','sdga' union select
'003','hahasg' union select
'003','gdsag'
select a.type,a.detail
from @t a
join @t b
on a.type= b.type
group by a.type,a.detail
having count(case when a.detail <= b.detail then 1 else null end) < = 2 --可动态修改
order by a.type asc
/*
type detail
---- ----------
001 gssfa
001 sss
002 fs
002 gahas
003 hahasg
003 sdga
(所影响的行数为 6 行)
*/
select a.* from @t a
where exists (select count(*)
from @t
where type = a.type and detail > a.detail having Count(*) < 2)
order by a.type
/*
type detail
---- ----------
001 gssfa
001 sss
002 fs
002 gahas
003 hahasg
003 sdga
(所影响的行数为 6 行)
*/
select a.* from @t a
where exists (select count(*)
from @t
where type = a.type and detail < a.detail having Count(*) < 2)
order by a.type
/*
type detail
---- ----------
001 a
001 gssfa
002 fdsf
002 fs
003 gdsag
003 hahasg
(所影响的行数为 6 行)
*/
select a.*
from @t a
where detail in (select top 2 detail
from @t where type=a.type
order by detail desc)
order by a.type,a.detail
/*
type detail
---- ----------
001 gssfa
001 sss
002 fs
002 gahas
003 hahasg
003 sdga
(所影响的行数为 6 行)
*/
select a.*
from @t a
where detail in (select top 2 detail
from @t where type=a.type
order by detail asc)
order by a.type,a.detail
/*
type detail
---- ----------
001 a
001 gssfa
002 fdsf
002 fs
003 gdsag
003 hahasg
(所影响的行数为 6 行)
*/
方法4:
select top 10 m.id as id, rtrim(left(title,11)) as titles,Clicks,AddTime,Auther,meno,Classes,s.phone as phone,s.name as name from
(select t.* from tb t where refreshtime = (select max(OrderCol) from tb where userid = t.userid) ) m
inner joinUserTable on s.userid=m.useridwhere m.id = (select max(id) from
(select t.* from tb t where OrderCol = (select max(OrderCol) from tb where isshow=0 and userid =t.userid)) n
where m.userid =n.userid)
order by OrderColdesc
--处理表重复记录(查询和删除)
/******************************************************************************************************************************************************
1、Num、Name相同的重复值记录,没有大小关系只保留一条
2、Name相同,ID有大小关系时,保留大或小其中一个记录
整理人:中国风(Roy)
日期:2008.06.06
******************************************************************************************************************************************************/
--1、用于查询重复处理记录(如果列没有大小关系时2000用生成自增列和临时表处理,SQL2005用row_number函数处理)
--> --> (Roy)生成測試數據
if not object_id('Tempdb..#T') is null
drop table #T
Go
Create table #T([ID] int,[Name] nvarchar(1),[Memo] nvarchar(2))
Insert #T
select 1,N'A',N'A1' union all
select 2,N'A',N'A2' union all
select 3,N'A',N'A3' union all
select 4,N'B',N'B1' union all
select 5,N'B',N'B2'
Go
--I、Name相同ID最小的记录(推荐用1,2,3),方法3在SQl05时,效率高于1、2
方法1:
Select * from #T a where not exists(select 1 from #T where Name=a.Name and ID<a.ID)
方法2:
select a.* from #T a join (select min(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID
方法3:
select * from #T a where ID=(select min(ID) from #T where Name=a.Name)
方法4:
select a.* from #T a join #T b on a.Name=b.Name and a.ID>=b.ID group by a.ID,a.Name,a.Memo having count(1)=1
方法5:
select * from #T a group by ID,Name,Memo having ID=(select min(ID)from #T where Name=a.Name)
方法6:
select * from #T a where (select count(1) from #T where Name=a.Name and ID<a.ID)=0
方法7:
select * from #T a where ID=(select top 1 ID from #T where Name=a.name order by ID)
方法8:
select * from #T a where ID!>all(select ID from #T where Name=a.Name)
方法9(注:ID为唯一时可用):
select * from #T a where ID in(select min(ID) from #T group by Name)
--SQL2005:
方法10:
select ID,Name,Memo from (select *,min(ID)over(partition by Name) as MinID from #T a)T where ID=MinID
方法11:
select ID,Name,Memo from (select *,row_number()over(partition by Name order by ID) as MinID from #T a)T where MinID=1
生成结果:
/*
ID Name Memo
----------- ---- ----
1 A A1
4 B B1
(2 行受影响)
*/
--II、Name相同ID最大的记录,与min相反:
方法1:
Select * from #T a where not exists(select 1 from #T where Name=a.Name and ID>a.ID)
方法2:
select a.* from #T a join (select max(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID order by ID
方法3:
select * from #T a where ID=(select max(ID) from #T where Name=a.Name) order by ID
方法4:
select a.* from #T a join #T b on a.Name=b.Name and a.ID<=b.ID group by a.ID,a.Name,a.Memo having count(1)=1
方法5:
select * from #T a group by ID,Name,Memo having ID=(select max(ID)from #T where Name=a.Name)
方法6:
select * from #T a where (select count(1) from #T where Name=a.Name and ID>a.ID)=0
方法7:
select * from #T a where ID=(select top 1 ID from #T where Name=a.name order by ID desc)
方法8:
select * from #T a where ID!<all(select ID from #T where Name=a.Name)
方法9(注:ID为唯一时可用):
select * from #T a where ID in(select max(ID) from #T group by Name)
--SQL2005:
方法10:
select ID,Name,Memo from (select *,max(ID)over(partition by Name) as MinID from #T a)T where ID=MinID
方法11:
select ID,Name,Memo from (select *,row_number()over(partition by Name order by ID desc) as MinID from #T a)T where MinID=1
生成结果2:
/*
ID Name Memo
----------- ---- ----
3 A A3
5 B B2
(2 行受影响)
*/
--2、删除重复记录有大小关系时,保留大或小其中一个记录
--> --> (Roy)生成測試數據
if not object_id('Tempdb..#T') is null
drop table #T
Go
Create table #T([ID] int,[Name] nvarchar(1),[Memo] nvarchar(2))
Insert #T
select 1,N'A',N'A1' union all
select 2,N'A',N'A2' union all
select 3,N'A',N'A3' union all
select 4,N'B',N'B1' union all
select 5,N'B',N'B2'
Go
--I、Name相同ID最小的记录(推荐用1,2,3),保留最小一条
方法1:
delete a from #T a where exists(select 1 from #T where Name=a.Name and ID<a.ID)
方法2:
delete a from #T a left join (select min(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID where b.Id is null
方法3:
delete a from #T a where ID not in (select min(ID) from #T where Name=a.Name)
方法4(注:ID为唯一时可用):
delete a from #T a where ID not in(select min(ID)from #T group by Name)
方法5:
delete a from #T a where (select count(1) from #T where Name=a.Name and ID<a.ID)>0
方法6:
delete a from #T a where ID<>(select top 1 ID from #T where Name=a.name order by ID)
方法7:
delete a from #T a where ID>any(select ID from #T where Name=a.Name)
select * from #T
生成结果:
/*
ID Name Memo
----------- ---- ----
1 A A1
4 B B1
(2 行受影响)
*/
--II、Name相同ID保留最大的一条记录:
方法1:
delete a from #T a where exists(select 1 from #T where Name=a.Name and ID>a.ID)
方法2:
delete a from #T a left join (select max(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID where b.Id is null
方法3:
delete a from #T a where ID not in (select max(ID) from #T where Name=a.Name)
方法4(注:ID为唯一时可用):
delete a from #T a where ID not in(select max(ID)from #T group by Name)
方法5:
delete a from #T a where (select count(1) from #T where Name=a.Name and ID>a.ID)>0
方法6:
delete a from #T a where ID<>(select top 1 ID from #T where Name=a.name order by ID desc)
方法7:
delete a from #T a where ID<any(select ID from #T where Name=a.Name)
select * from #T
/*
ID Name Memo
----------- ---- ----
3 A A3
5 B B2
(2 行受影响)
*/
--3、删除重复记录没有大小关系时,处理重复值
--> --> (Roy)生成測試數據
if not object_id('Tempdb..#T') is null
drop table #T
Go
Create table #T([Num] int,[Name] nvarchar(1))
Insert #T
select 1,N'A' union all
select 1,N'A' union all
select 1,N'A' union all
select 2,N'B' union all
select 2,N'B'
Go
方法1:
if object_id('Tempdb..#') is not null
drop table #
Select distinct * into # from #T--排除重复记录结果集生成临时表#
truncate table #T--清空表
insert #T select * from # --把临时表#插入到表#T中
--查看结果
select * from #T
/*
Num Name
----------- ----
1 A
2 B
(2 行受影响)
*/
--重新执行测试数据后用方法2
方法2:
alter table #T add ID int identity--新增标识列
go
delete a from #T a where exists(select 1 from #T where Num=a.Num and Name=a.Name and ID>a.ID)--只保留一条记录
go
alter table #T drop column ID--删除标识列
--查看结果
select * from #T
/*
Num Name
----------- ----
1 A
2 B
(2 行受影响)
*/
--重新执行测试数据后用方法3
方法3:
declare Roy_Cursor cursor local for
select count(1)-1,Num,Name from #T group by Num,Name having count(1)>1
declare @con int,@Num int,@Name nvarchar(1)
open Roy_Cursor
fetch next from Roy_Cursor into @con,@Num,@Name
while @@Fetch_status=0
begin
set rowcount @con;
delete #T where Num=@Num and Name=@Name
set rowcount 0;
fetch next from Roy_Cursor into @con,@Num,@Name
end
close Roy_Cursor
deallocate Roy_Cursor
--查看结果
select * from #T
/*
Num Name
----------- ----
1 A
2 B
(2 行受影响)
*/
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