看代码：

复制代码 代码如下:

set statistics io on

set statistics time on

go

set statistics profile on

go

use pubs

select * from authors

where (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 authors

where (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 authors

where (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。