SQL Server 2005改進后的幾個實用新特性
1. TOP 表達式
SQL Server 2000的TOP是個固定值,是不是覺得差強人意,現在改進了。
--前n名的訂單
declare @n int
set @n = 10
select TOP(@n) * from Orders
2. 分頁
不知大家過去用SQL Server 2000是如何分頁的,大多都用到了臨時表。SQL Server 2005就支持分頁,性能也非常不錯。
--按Freight從小到大排序,求20到30行的結果
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沒有異常,T-SQL必須逐行檢查錯誤代碼,對于習慣了try catch程序員,2005是不是更加親切:
SET XACT_ABORT ON -- 打開 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. 通用表達式CTE
通過表達式可以免除你過去創建臨時表的麻煩。
例:結合通用表達式進行分頁
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
特別之處:通過表達式還可以支持遞歸。
