SQL中使用WITH AS提高性能（二）

继上一节

对比两条查询，第一是用了with as 第二条语句没用with as 查看执行计划的效果

WITH    vep
          AS ( SELECT   package.OrderCode ,
                        RANK() OVER ( PARTITION BY package.OrderCode ORDER BY package.ID ) AS Index ,
                        COUNT(1) OVER ( PARTITION BY package.OrderCode ) AS Count
               FROM     dbo.BookPackages package WITH ( NOLOCK )
             )
    SELECT TOP 100
            *
    FROM    vep
    WHERE   vep.Count > 2

　　

SELECT TOP 100 * FROM (
SELECT
	vep.OrderCode,
	ROW_NUMBER() OVER(PARTITION BY vep.OrderCode ORDER BY vep.ID ) 'Index',
	COUNT(1) OVER(PARTITION BY vep.OrderCode) 'Count'
FROM
	dbo.BookPackages 

vep WITH(NOLOCK) ) a WHERE a.Count>2

　　明显用了with as 快了很多

中间用到了 rank() over (partition by over by) 语句，下一篇再写