每个分类取5条, 这样的SQL怎么写？

每个分类取5条, 这样的SQL如何写？？
比如，假设我有这样的一个表 ： table1

表的结构如下：

SQL code

CREATE TABLE table1(    [ID] [bigint] IDENTITY(1,1) NOT NULL,    [Name] [nvarchar](128) NOT NULL,    [class] int not null,    [date] datetime not null)

class 表示分类编号。 分类数不固定， 至少有上千种分类
date 表示该条记录被更新的时间

我现在想获得每个分类最新被更新的5条记录。

我该如何写写这个SQL 语句？？


拼一个巨大的SQL 不太现实，因为分类太多了。

使用游标遍历每个分类，总觉得不是很好的方法。
谁有更好的方法呢？？




[解决办法]
select *
from table1 a
where 5>(select count(*) from table1 where class=a.class and date>=a.date)
[解决办法]

SQL code

select * from table1 as t where date in (select top 5 date from talbe1 where class=t.class order by date desc)
[解决办法]
SQL code
--按某一字段分组取最大(小)值所在行的数据(爱新觉罗.毓华 2007-10-23于浙江杭州)/*数据如下：name val memoa    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   b2b2b2b2b    4   b4b4b    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5select 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5select 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)valselect a.* from tb a where 2 > (select count(*) from tb where name = a.name and val < a.val ) order by a.name,a.valselect 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.valselect 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)valselect a.* from tb a where 2 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name,a.valselect 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.valselect 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           b4b4b          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 memoa    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   b2b2b2b2b    4   b4b4b    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)*/ 
 
[解决办法]
SQL code
select id,name,class,date from(select id,name,class,date ,row_number() over(partition by class order by date desc)as rowindex from table1)awhere rowindex<=5
[解决办法]
SQL code
数据如下：name val memoa    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   b2b2b2b2b    4   b4b4b    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--五、按name分组取最小的两个(N个)valselect a.* from tb a where 2 > (select count(*) from tb where name = a.name and val < a.val ) order by a.name,a.valselect 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.valselect 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)valselect a.* from tb a where 2 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name,a.valselect 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.valselect 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           b4b4b          5           b5b5b5b5b5*/
[解决办法]
SQL code
CREATE TABLE table1(    [ID] [bigint] IDENTITY(1,1) NOT NULL,    [Name] [nvarchar](128) NOT NULL,    [class] int not null,    [date] datetime not null)----------------------select * from table1 a where id in(select top 5 id from table1 where class=a.class order by date desc)
[解决办法]
探讨

SQL codeselect id,name,class,date from(
select id,name,class,date ,row_number() over(partition by class order by date desc)
as rowindex from table1)a
where rowindex<=5
 

 

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