create table table1(id int identity(1,1),number char(5))
insert into table1 values('DF001')
insert into table1 values('DF005')
insert into table1 values('DC001')
insert into table1 values('DF005')
update table1 set number=replace(number,'DF','DT')
select * from table1
/*结果
id number
---------------------------------------------------
1 DT001
2 DT005
3 DC001
4 DT005