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。
