SQL比较两个日期的最快方法(非标准varchar格式和datetime)

yyyy-mm-dd hh:mm:ss

第二个是红头step-child格式的varchar(8) mmddyyyy

现在这会很痛苦,因为没有简单的方法可以转换为相应的类型。有一种内置格式 yyyymmdd

declare @normal_date as datetime;
declare @hated_date as varchar(8);

set @normal_date='1974-11-01 00:00:00.000'
set @hated_date='11011974'

--cast to date time with string splits
select @normal_date
where CONVERT(datetime, RIGHT(@hated_date,4)+LEFT(@hated_date,2)+SUBSTRING(@hated_date,3,2))=@normal_date

--convert normal date to ackward format
select @normal_date
      where REPLACE(CONVERT(varchar(10),@normal_date,101), '/','')=@hated_date

哪个更好?还是有更好的办法?

编辑以显示成本

--Operator cost (39%)
CONVERT(datetime, RIGHT(@hated_date,4)+LEFT(@hated_date,2)+SUBSTRING(@hated_date,3,2))=@normal_date

--Operator cost (57%)
REPLACE(CONVERT(varchar(10),@normal_date,101), '/','')=@hated_date

--Operator cost (46%)
cast(stuff(stuff(@hated_date, 3,0, '/'),6,0,'/') as datetime)=@normal_date

--Operator cost (47%)
RIGHT(@hated_date, 4) + LEFT(@hated_date, 4)=@normal_date