Question

I’m using SQL Server 2008.

I have two Tables: User_master and Item_master.

There is a User with user_id = 10.

|---------|
| user_id |
|---------|
|   10    |
|---------|

There are 5 Items with item_id = 20 to 24.

|---------|---------|------------|
| item_id | user_id | item_order |
|---------|---------|------------|
|   20    |    10   |     0      |
|---------|---------|------------|
|   21    |    10   |     0      |
|---------|---------|------------|
|   22    |    10   |     0      |
|---------|---------|------------|
|   23    |    10   |     0      |
|---------|---------|------------|
|   24    |    10   |     0      |
|---------|---------|------------|

There is one more column in Item_master that is item_order(int).
I want to place item_order = 0 to 4 in all these rows with only single query.

Is it possible?

EDIT :

item_id is not supposed to be in order.

For example, instead of 20,21,22,23,24; it could be 20,25,31,47,58.

Answer 1

You can use the row_number() window function to assign an increasing number to each row with the same user_id. A subquery is required because you cannot use window functions directly in the set clause.

update  im
set     im.item_order = im.rn
from    (
        select  row_number() over (partition by user_id
                                   order by item_id) - 1 as rn
        ,       *
        from    item_master
        ) as im;

Live example at SQL Fiddle.