SQL Server实现查询每个分组的前N条记录

SQL语句查询每个分组的前N条记录的实现方法：

1、生成测试数据: #T

if object_id("tempdb.dbo.#T") is not null drop table #T;

create table #T (ID varchar(3),
GID int,
Author varchar(29),
Title varchar(39),
Date datetime);

insert into #T
select "001", 1, "邹建", "深入浅出SQLServer2005开发管理与应用实例", "2008-05-10"
union all
select "002", 1, "胡百敬", "SQLServer2005性能调校", "2008-03-22"
union all
select "003", 1, "格罗夫Groff.J.R.", "SQL完全手册", "2009-07-01"
union all
select "004", 1, "KalenDelaney", "SQLServer2005技术内幕存储引擎", "2008-08-01"
union all
select "005", 2, "Alex.Kriegel.Boris.M.Trukhnov", "SQL宝典", "2007-10-05"
union all
select "006", 2, "飞思科技产品研发中心", "SQLServer2000高级管理与开发", "2007-09-10"
union all
select "007", 2, "胡百敬", "SQLServer2005数据库开发详解", "2008-06-15"
union all
select "008", 3, "陈浩奎", "SQLServer2000存储过程与XML编程", "2005-09-01"
union all
select "009", 3, "赵松涛", "SQLServer2005系统管理实录", "2008-10-01"
union all
select "010", 3, "黄占涛", "SQL技术手册", "2006-01-01"
union all
select "010", 4, "黄蛋蛋", "SQL技术手册蛋蛋", "2006-01-01";

2、表记录查询如下:

select * from #T;

结果：

3、按GID分组,查每个分组中Date最新的前2条记录

（1）用子查询

--1.字段ID唯一时: 
select *
from #T as T
where ID in (select top 2 ID from #T where GID=T.GID order by Date desc);

--2.如果ID不唯一时: 
select *
from #T as T
where 2>(select count(*)from #T where GID=T.GID and Date>T.Date);

（2）使用SQL Server 2005 使用新方法ROW_NUMBER()进行排位分组

select ID, GID, Author, Title, Date
from(
       select rid=row_number() over (partition by GID order by Date desc), * from #T) as T
where rid<=2;

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