where-子句的执行顺序

看代码：

复制代码 代码如下:

set statistics io onset statistics time ongoset statistics profile ongouse pubsselect * from authorswhere (au_fname like 'S%' or au_fname like 'a%')and (state like 'CA' or state like 'UT')and (cast(zip as int) > 90000)select * from authorswhere (au_fname like 'S%' or au_fname like 'a%')and (cast(zip as int) > 90000)and (state like 'CA' or state like 'UT')select * from authorswhere (cast(zip as int) > 90000)and (au_fname like 'S%' or au_fname like 'a%')and (state like 'CA' or state like 'UT')

目的：想验证where语句的各个条件的查询顺序环境：SQLserver 2005Express版本步骤：显示查询计划结果：无一例外，都被统一成了这样的代码

复制代码 代码如下:

|--Clustered Index Scan(OBJECT:([pubs].[dbo].[authors].[UPKCL_auidind]), WHERE:(CONVERT(int,[pubs].[dbo].[authors].[zip],0)>(90000) AND ([pubs].[dbo].[authors].[au_fname] like 'S%' OR [pubs].[dbo].[authors].[au_fname] like 'a%') AND ([pubs].[dbo].[authors].[state] like 'CA' OR [pubs].[dbo].[authors].[state] like 'UT')))

结论：貌似在2005之前的版本中，where子句的顺序是从前往后的。但是又貌似在2005的版本中进行了优化，所有的顺序都被统一成了以过滤能力进行排序的语句。