利用sql2005的新特性实现根据子表条件得到的主表键且按其排序取出对应主子表记录的方法_数据库技巧

假如有两个关联表，是一对多关系的主子表。如下：

主表

CREATE TABLE [dbo].[CourseT](
    [CourseID] [int] IDENTITY(1,1) NOT NULL,
    [CourseName] [nchar](10) COLLATE Chinese_PRC_CI_AS_WS NULL
) ON [PRIMARY]

字表

CREATE TABLE [dbo].[Broad](
    [BroadID] [int] IDENTITY(1,1) NOT NULL,
    [CourseID] [int] NULL,
    [BroadName] [nvarchar](50) COLLATE Chinese_PRC_CI_AS_WS NULL
) ON [PRIMARY]

如果数据取自CourseT表，我们想查询Broad表中记录对应的CourseT表中的记录，且按CourseID的降序只取一次，在SQL2005中SQL如下

with temp as
(
select distinct courseid from Broad
),
 temp2 as
(
    select courseid , ROW_NUMBER() OVER(ORDER BY courseid desc) AS row_num
     from temp
)
select CourseT.* from  CourseT, temp2 where courset.courseid=temp2.courseid order by row_num

如果数据取自CourseT和Broad表，我们想查询Broad表中记录对应的CourseT表中的记录，且按CourseID的降序只取一次，我们可以如下写：

with temp as
(
  select courseid, broadid, row_number() over(order by courseid desc, broadid desc  ) as rownum from broad
),
temp2 as
(
select temp.courseid, temp.broadid from temp where rownum=1
union
select temp.courseid, temp.broadid from temp, temp as temp0 where temp.rownum = temp0.rownum+1 and temp.courseid <> temp0.courseid
)

select CourseT.*, broad.broadid, broad.broadname from  CourseT, broad, temp2
 where courset.courseid=broad.courseid and temp2.courseid = courset.courseid and temp2.broadid = broad.broadid order by
broad.courseid desc ,broad.broadid desc
经牛人宪哥帮忙，又想出一个更好的方案如下：
select CourseT.CourseID,CourseName,b.BroadID,b.BroadName
 from CourseT,broad b,(select max(broadid) bid,CourseID from broad group by courseid ) t
  where
   CourseT.CourseID=b.CourseId and b.CourseID=t.courseid and b.broadid=t.bid
http://www.cnblogs.com/laiwen/archive/2006/12/30/607690.html