数据库自定义方法及在Sql语句中调用

由于 在我使用的数据表中 lasttime字段 在写入数据表时写入字符串‘20120401145112827’类型 在业务中需要对其字段时间做处理  以下过程是使用数据库自定义方法 简化Sql语句

--Sql中自定义方法
create function StrToDateTime(@DateStr as varchar(18))
returns varchar(24) --注意 returns 不是 return 
as
begin
	declare @date varchar(24);
	set @date=@DateStr;
	set @date=(SUBSTRING(cast (@date as varchar(18)),1,4)+'-'+SUBSTRING(cast (@date as varchar(18)),5,2) +'-'+SUBSTRING(cast (@date as varchar(18)),7,2)
		   +' '+SUBSTRING(cast (@date as varchar(18)),9,2)
		   +':'+SUBSTRING(cast (@date as varchar(18)),11,2)
		   +':'+SUBSTRING(cast (@date as varchar(18)),13,2));
	return @date;
end

declare @returntime varchar(24)
exec @returntime=StrToDateTime '20120401145112827'
print convert(varchar(24),convert(datetime,@returntime),20)


--初始Sql语句  未使用自定义方法
select * from (
select id,interID,cpid,intername,reply,lasttime,CASE lasttime
         WHEN '0' THEN getdate()-3
	     Else cast((SUBSTRING(cast (lasttime as varchar(18)),1,4)
+'-'+SUBSTRING(cast (lasttime as varchar(18)),5,2)
+'-'+SUBSTRING(cast (lasttime as varchar(18)),7,2)
+' '+SUBSTRING(cast (lasttime as varchar(18)),9,2)
+':'+SUBSTRING(cast (lasttime as varchar(18)),11,2)
+':'+SUBSTRING(cast (lasttime as varchar(18)),13,2)
) as varchar(24))
         end  as ldate,setTime  from xsreuserinter 
) as temp
 where (datediff(hh,temp.ldate,getdate())>72 and datediff(hh,temp.setTime,getdate())>72) order by lasttime desc

--调用该方法之后的Sql语句  
--Notice: 调用该方法时 一定要加前缀dbo. 否则 报错“该内置方法不识别” 该方法在哪个数据库下执行 只属于哪个数据库 跨数据库无效
--调用方法为 select dbo.StrToDateTime(lasttime)
select * from (
select id,interID,cpid,intername,reply,lasttime,CASE lasttime
         WHEN '0' THEN getdate()-3
	     Else convert(datetime,dbo.StrToDateTime(lasttime),20) --该处调用function
         end  as ldate,setTime  from xsreuserinter 
) as temp
 where (datediff(hh,temp.ldate,getdate())>72 and datediff(hh,temp.setTime,getdate())>72) order by lasttime desc