create table wan(pic varchar(100))

insert into wan
select '20054181241305.jpg' union all
select '/productFiles/2007-10/20071012154826320.gif'


update wan set pic='/productFiles/'
+reverse(substring(reverse(pic),1,len(pic)-charindex('/',reverse(pic),1)))

select * from wan
/*
pic
---------------------------------------
/productFiles/20054181241305.jpg
/productFiles/20071012154826320.gif

(2 row(s) affected)
*/

------解决方案--------------------

SQL code
create table ta(pic varchar(128))
insert ta 
select '20054181241305.jpg' 
union select '/productFiles/2007-10/20071012154826320.gif'

select * from ta 
/*
pic
20054181241305.jpg
/productFiles/2007-10/20071012154826320.gif  
*/
update ta set pic =case when CHARINDEX('/',pic,0)=0 then '/productFiles/'+pic  else '/productFiles/'+reverse(substring(reverse(pic),1,charindex('/',reverse(pic),1)-1))
 end 

/*
pic
/productFiles/20054181241305.jpg
/productFiles/20071012154826320.gif  
*/
drop table ta