取每一类(classid)点击次数(hits)最多的一条记录，要求输出所有列
table
id name classid hits
1 aaa 1 54
2 bbb 1 80
3 ccc 1 96
4 ddd 2 12
5 eee 2 65
6 fff 2 43
7 ggg 3 102
8 iii 3 76
9 hhh 3 56
table
id name classid hits
1 aaa 1 54
2 bbb 1 80
3 ccc 1 96
4 ddd 2 12
5 eee 2 65
6 fff 2 43
7 ggg 3 102
8 iii 3 76
9 hhh 3 56
(爱新觉罗.毓华 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
/*
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
/*
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)
*/
where id=(select top 1 id from tab where classid=a.classid order by hits desc)
from table a
where not exists(select 1 from table where a.classid = classid and hits > a.hits)
where not exists (select 1 from tab where classid=a.classid and hits>a.hits)
if object_id('tempdb.dbo.#table1') is not null drop table #table1
create table #table1 (id int,name varchar(3),classid int,hits int)
insert into #table1
select 1,'aaa',1,54 union all
select 2,'bbb',1,80 union all
select 3,'ccc',1,96 union all
select 4,'ddd',2,12 union all
select 5,'eee',2,65 union all
select 6,'fff',2,43 union all
select 7,'ggg',3,102 union all
select 8,'iii',3,76 union all
select 9,'hhh',3,56select a.* from #table1 as a
inner join
(
select classid,max(hits) as hits from #table1 group by classid
) as b on a.classid=b.classid and a.hits=b.hits/*
---------------
7 ggg 3 102
5 eee 2 65
3 ccc 1 96
*/
select * from table t where not exists(select 1 from table where classid=t.classid and hits>t.hits)
declare @tb table([id] int,[name] nvarchar(3),[classid] int,[hits] int)
Insert @tb
select 1,N'aaa',1,54 union all
select 2,N'bbb',1,80 union all
select 3,N'ccc',1,96 union all
select 4,N'ddd',2,12 union all
select 5,N'eee',2,65 union all
select 6,N'fff',2,43 union all
select 7,N'ggg',3,102 union all
select 8,N'iii',3,76 union all
select 9,N'hhh',3,56
Select * from @tb a
where not exists (select 1 from @tb where [classid] = a.[classid] and [hits]>a.[hits])
/*
id name classid hits
----------- ---- ----------- -----------
3 ccc 1 96
5 eee 2 65
7 ggg 3 102
*/
from table
where hits=(select maxhits from table group by classid)
if object_id('tempdb.dbo.#table1') is not null drop table #table1
create table #table1 (id int,name varchar(3),classid int,hits int)
insert into #table1
select 1,'aaa',1,54 union all
select 2,'bbb',1,80 union all
select 3,'ccc',1,96 union all
select 4,'ddd',2,12 union all
select 5,'eee',2,65 union all
select 6,'fff',2,43 union all
select 7,'ggg',3,102 union all
select 8,'iii',3,76 union all
select 9,'hhh',3,56
;with tb
as
(
SELECT *,rw = ROW_NUMBER() OVER (PARTITION BY classid ORDER BY hits DESC) FROM #table1
)
SELECT id,name,classid,hits FROM tb WHERE rw = 1/*id name classid hits
3 ccc 1 96
5 eee 2 65
7 ggg 3 102
*/