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SQL Server 2005实用新特性

Jun 07, 2016 pm 03:05 PM
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SQL Server 2005 相对于 SQL Server 2000 做了很大的改进,许些新 特性 是非常 实用 的。本文中将通过几个具体示例进行详细的说明。( 这些例子引用Northwind库) 1. TOP 表达式 SQL Server 2000的TOP是个固定值,是不是觉得差强人意,现在改进了。 --前n名的

  SQL Server 2005相对于SQL Server 2000做了很大的改进,许些新特性是非常实用的。本文中将通过几个具体示例进行详细的说明。( 这些例子引用Northwind库)

  1. TOP 表达式

  SQL Server 2000的TOP是个固定值,是不是觉得差强人意,现在改进了。

  --前n名的订单

  declare @n int

  set @n = 10

  select TOP(@n) * from Orders

  2. 分页

  不知大家过去用SQL Server 2000是如何分页的,大多都用到了临时表。SQL Server 2005就支持分页,性能也非常不错。

  --按Freight从小到大排序,求20到30行的结果

  select * from(select OrderId, Freight, ROW_NUMBER() OVER(order by Freight) as row from Orders) a

  where row between 20 and 30

  3. 排名

  select * from(select OrderId, Freight, RANK() OVER(order by Freight) as rank from Orders) a

  where rank between 20 and 30

  4. try ... catch

  SQL Server 2000没有异常,T-SQL必须逐行检查错误代码,对于习惯了try catch程序员,2005是不是更加亲切:

  SET XACT_ABORT ON -- 打开 try功能

  BEGIN TRY

  begin tran

  insert into Orders(CustomerId) values(-1)

  commit tran

  print 'commited'

  END TRY

  BEGIN CATCH

  rollback

  print 'rolled back'

  END CATCH

  5. 通用表达式CTE

  通过表达式可以免除你过去创建临时表的麻烦。

  例:结合通用表达式进行分页

  WITH OrderFreight AS(

  select OrderId, Freight, ROW_NUMBER() OVER(order by Freight) as row from Orders

  )

  select OrderId, Freight from OrderFreight where row between 10 and 20

  特别之处:通过表达式还可以支持递归.

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