--> 测试数据：[tbl]
if object_id('[tbl]') is not null drop table [tbl]
create table [tbl]([ID] int,[Code] int)
insert [tbl]
select 1,123 union all
select 2,123 union all
select 4,123 union all
select 6,1234 union all
select 7,1234
--2005以上版本
select *,
ROW_NUMBER()over(partition by [Code] order by getdate())as row_num
from tbl
--2000版本
select *,
row_num=(select COUNT(*) from tbl a 
where a.Code=b.Code and a.ID<=b.ID) from tbl b
/*
ID    Code    row_num
1    123    1
2    123    2
4    123    3
6    1234    1
7    1234    2
*