取得同一类别中，时间最近的一段数据
比如Tables
id Type Date
1 1 2007-10-11 12:34:10
2 1 2007-10-12 12:34:10
3 1 2007-10-13 12:34:10
4 2 2007-10-14 12:34:10
5 2 2007-10-15 12:34:10
6 3 2007-10-16 12:34:10
7 3 2007-10-17 12:34:10
8 3 2007-10-18 12:34:10
我想取的数据
id Type Date
1 1 2007-10-13 12:34:10
5 2 2007-10-15 12:34:10
8 3 2007-10-18 12:34:10sql语句怎么写啊。各位帮帮忙
比如Tables
id Type Date
1 1 2007-10-11 12:34:10
2 1 2007-10-12 12:34:10
3 1 2007-10-13 12:34:10
4 2 2007-10-14 12:34:10
5 2 2007-10-15 12:34:10
6 3 2007-10-16 12:34:10
7 3 2007-10-17 12:34:10
8 3 2007-10-18 12:34:10
我想取的数据
id Type Date
1 1 2007-10-13 12:34:10
5 2 2007-10-15 12:34:10
8 3 2007-10-18 12:34:10sql语句怎么写啊。各位帮帮忙
insert @t select 1,'1','2007-10-11 12:34:10'
insert @t select 2,'1','2007-10-12 12:34:10'
insert @t select 3,'2','2007-10-13 12:34:10'
insert @t select 4,'2','2007-10-14 12:34:10'
insert @t select 5,'3','2007-10-15 12:34:10'
insert @t select 6,'3','2007-10-16 12:34:10'
select
t.*
from
@t t
where
t.Date=(select max(Date) from @t where Type=t.Type)2，3高！
create table t1(
id int,
Type int,
Date datetime
)insert into t1
select 1 , 1 , '2007-10-11 12:34:10' union all
select 2 , 1 , '2007-10-12 12:34:10' union all
select 3 , 1 , '2007-10-13 12:34:10' union all
select 4 , 2 , '2007-10-14 12:34:10' union all
select 5 , 2 , '2007-10-15 12:34:10' union all
select 6 , 3 , '2007-10-16 12:34:10' union all
select 7 , 3 , '2007-10-17 12:34:10' union all
select 8 , 3 , '2007-10-18 12:34:10'select * from t1select max(id) as [id],type,max(date) as [date]
from t1
group by type/*
id type date
----------- ----------- ------------------------------------------------------
3 1 2007-10-13 12:34:10.000
5 2 2007-10-15 12:34:10.000
8 3 2007-10-18 12:34:10.000（所影响的行数为 3 行）
*/
/*
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
*/
insert into tb values(1, 1, '2007-10-11 12:34:10')
insert into tb values(2, 1, '2007-10-12 12:34:10')
insert into tb values(3, 1, '2007-10-13 12:34:10')
insert into tb values(4, 2, '2007-10-14 12:34:10')
insert into tb values(5, 2, '2007-10-15 12:34:10')
insert into tb values(6, 3, '2007-10-16 12:34:10')
insert into tb values(7, 3, '2007-10-17 12:34:10')
insert into tb values(8, 3, '2007-10-18 12:34:10')
goselect a.* from tb a where date = (select max(Date) from tb where type = a.type) order by a.typedrop table tb/*
id Type Date
----------- ----------- ------------------------------------------------------
3 1 2007-10-13 12:34:10.000
5 2 2007-10-15 12:34:10.000
8 3 2007-10-18 12:34:10.000（所影响的行数为 3 行）
*/
select * from t a
where not exists(select 1 from t where type=a.type and date<a.date)