Question

I am trying to wrap my head around a problem I hit exporting data from one system to another.

Let’s say I have a table like:

id  |  item_num  
1      1            
2      1            
3      2            
4      3            
5      3           
6      3            

I need to add a column to the table and update it to contain an incrementing product_num field based on item. This would be the end result given the above table.

id  |  item_num  |  product_num
1      1            1
2      1            2
3      2            1
4      3            1
5      3            2
6      3            3 

Any ideas on going about this?

Edit: This is being done in Access 2010 from one system to another (sql server source, custom/unknown ODBC driven destination)

Answer 1

Perhaps you could create a view in your SQL Server database and then select from that in Access to insert into your destination.

Possible solutions in SQL Server:

-- Use row_number() to get product_num in SQL Server 2005+:
select id
    , item_num
    , row_number() over (partition by item_num order by id) as product_num
from MyTable;

-- Use a correlated subquery to get product_num in many databases:
select t.id
    , t.item_num
    , (select count(*) from MyTable where item_num = t.item_num and id <= t.id) as product_num
from MyTable t;

Same result:

id          item_num    product_num
----------- ----------- --------------------
1           1           1
2           1           2
3           2           1
4           3           1
5           3           2
6           3           3