上面标题可能不能表述清楚,这里详细说明一下:
有一表Assets, 字段如下: User, ComputerName, Os, MacAddress,ModifyDate
这个表是无主键的,这个条件很特殊,确定此表的唯一性是根据MacAddress和ModifyDate两个字段来的.MacAddress有重复的值, 要求查找表的所有记录,(MacAddress不能有复复, ModifyDate选择在所有MacAddress重复时最大值)假设数据表记录如下:User ComputerName, Os, MacAddress, ModifyDateA AName xp H5:3B:0C 2009-10-02 21:37:22
B BName xp H5:3B:0C 2009-10-05 21:37:22
C CName xp G6:3B:0C 2009-09-02 21:37:22
D DName xp F2:9D:0C 2009-09-18 17:31:28
E EName xp W6:08:0K 2009-10-15 05:59:22
D DName xp F2:9D:0C 2009-09-19 21:37:22
F DName xp F2:9D:0C 2009-10-07 11:08:10 那么我要拿的数据应该是:
B BName xp H5:3B:0C 2009-10-05 21:37:22
C CName xp G6:3B:0C 2009-09-02 21:37:22
E EName xp W6:08:0K 2009-10-15 05:59:22
D DName xp F2:9D:0C 2009-10-07 11:08:10
有一表Assets, 字段如下: User, ComputerName, Os, MacAddress,ModifyDate
这个表是无主键的,这个条件很特殊,确定此表的唯一性是根据MacAddress和ModifyDate两个字段来的.MacAddress有重复的值, 要求查找表的所有记录,(MacAddress不能有复复, ModifyDate选择在所有MacAddress重复时最大值)假设数据表记录如下:User ComputerName, Os, MacAddress, ModifyDateA AName xp H5:3B:0C 2009-10-02 21:37:22
B BName xp H5:3B:0C 2009-10-05 21:37:22
C CName xp G6:3B:0C 2009-09-02 21:37:22
D DName xp F2:9D:0C 2009-09-18 17:31:28
E EName xp W6:08:0K 2009-10-15 05:59:22
D DName xp F2:9D:0C 2009-09-19 21:37:22
F DName xp F2:9D:0C 2009-10-07 11:08:10 那么我要拿的数据应该是:
B BName xp H5:3B:0C 2009-10-05 21:37:22
C CName xp G6:3B:0C 2009-09-02 21:37:22
E EName xp W6:08:0K 2009-10-15 05:59:22
D DName xp F2:9D:0C 2009-10-07 11:08:10
--按某一字段分组取最大(小)值所在行的数据
--(爱新觉罗.毓华(十八年风雨,守得冰山雪莲花开) 2007-10-23于浙江杭州)
/*
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 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', 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--一、按name分组取val最大的值所在行的数据。
--方法1:
select a.* from tb a where val = (select max(val) from tb where name = a.name) order by a.name
--方法2:
select a.* from tb a where not exists(select 1 from tb where name = a.name and val > a.val)
--方法3:
select a.* from tb a,(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 tb a 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 tb a where val = (select min(val) from tb where name = a.name) order by a.name
--方法2:
select a.* from tb a where not exists(select 1 from tb where name = a.name and val < a.val)
--方法3:
select a.* from tb a,(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 tb a 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 tb a 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 tb a 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,a.val
/*
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 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 desc) 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 , a.val
/*
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')
goselect * , px = identity(int,1,1) into tmp from tbselect 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')
goselect 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)
*/
select t.* from tb where not exists(select 1 from tb where MacAddress = t.MacAddress and ModifyDate > t.ModifyDate)
*
from
tb t
where
not exists(select 1 from tb where MacAddress = t.MacAddress and ModifyDate > t.ModifyDate)
insert into tb values('A' , 'AName' , 'xp' , 'H5:3B:0C' , '2009-10-02 21:37:22')
insert into tb values('B' , 'BName' , 'xp' , 'H5:3B:0C' , '2009-10-05 21:37:22')
insert into tb values('C' , 'CName' , 'xp' , 'G6:3B:0C' , '2009-09-02 21:37:22')
insert into tb values('D' , 'DName' , 'xp' , 'F2:9D:0C' , '2009-09-18 17:31:28')
insert into tb values('E' , 'EName' , 'xp' , 'W6:08:0K' , '2009-10-15 05:59:22')
insert into tb values('D' , 'DName' , 'xp' , 'F2:9D:0C' , '2009-09-19 21:37:22')
insert into tb values('F' , 'DName' , 'xp' , 'F2:9D:0C' , '2009-10-07 11:08:10')
go
select t.* from tb t where ModifyDate = (select max(ModifyDate) from tb where MacAddress = t.MacAddress) order by t.[user]
/*
User ComputerName Os MacAddress ModifyDate
---------- ------------ ---------- ---------- ------------------------------------------------------
B BName xp H5:3B:0C 2009-10-05 21:37:22.000
C CName xp G6:3B:0C 2009-09-02 21:37:22.000
E EName xp W6:08:0K 2009-10-15 05:59:22.000
F DName xp F2:9D:0C 2009-10-07 11:08:10.000(所影响的行数为 4 行)
*/select t.* from tb t where not exists(select 1 from tb where MacAddress = t.MacAddress and ModifyDate > t.ModifyDate) order by t.[user]
/*
User ComputerName Os MacAddress ModifyDate
---------- ------------ ---------- ---------- ------------------------------------------------------
B BName xp H5:3B:0C 2009-10-05 21:37:22.000
C CName xp G6:3B:0C 2009-09-02 21:37:22.000
E EName xp W6:08:0K 2009-10-15 05:59:22.000
F DName xp F2:9D:0C 2009-10-07 11:08:10.000(所影响的行数为 4 行)
*/drop table tb
create table Assets (username char(1), ComputerName varchar(10), Os varchar(5), MacAddress varchar(20), ModifyDate datetime)go
insert into Assets values('A','AName','xp','H5:3B:0C','2009-10-02 21:37:22')
insert into Assets values('B','BName','xp','H5:3B:0C','2009-10-05 21:37:22')
insert into Assets values('C','CName','xp','G6:3B:0C','2009-09-02 21:37:22')
insert into Assets values('D','DName','xp','F2:9D:0C','2009-09-18 17:31:28')
insert into Assets values('E','EName','xp','W6:08:0K','2009-10-15 05:59:22')
insert into Assets values('D','DName','xp','F2:9D:0C','2009-09-19 21:37:22')
insert into Assets values('F','DName','xp','F2:9D:0C','2009-10-07 11:08:10')GOselect a.* from assets a where modifydate = (select max(b.modifydate) from assets b where b.macaddress = a.macaddress) order by macaddressGO
DROP TABLE Assets