Question

Let’s say I have a Product table in a shopping site’s database to keep description, price, etc of store’s products. What is the most efficient way to make my client able to re-order these products?

I create an Order column (integer) to use for sorting records but that gives me some headaches regarding performance due to the primitive methods I use to change the order of every record after the one I actually need to change. An example:

Id    Order
5     3
8     1
26    2
32    5
120   4

Now what can I do to change the order of the record with ID=26 to 3?

What I did was creating a procedure which checks whether there is a record in the target order (3) and updates the order of the row (ID=26) if not. If there is a record in target order the procedure executes itself sending that row’s ID with target order + 1 as parameters.

That causes to update every single record after the one I want to change to make room:

Id    Order
5     4
8     1
26    3
32    6
120   5

So what would a smarter person do?

• I use SQL Server 2008 R2.

Edit:

I need the order column of an item to be enough for sorting with no secondary keys involved. Order column alone must specify a unique place for its record.

In addition to all, I wonder if I can implement something like of a linked list: A ‘Next’ column instead of an ‘Order’ column to keep the next items ID. But I have no idea how to write the query that retrieves the records with correct order. If anyone has an idea about this approach as well, please share.

Answer 1

Update product set order = order+1 where order >= @value changed

Though over time you’ll get larger and larger “spaces” in your order but it will still “sort”

This will add 1 to the value being changed and every value after it in one statement, but the above statement is still true. larger and larger “spaces” will form in your order possibly getting to the point of exceeding an INT value.

Alternate solution given desire for no spaces:

Imagine a procedure for: UpdateSortOrder with parameters of @NewOrderVal, @IDToChange,@OriginalOrderVal

Two step process depending if new/old order is moving up or down the sort.

If @NewOrderVal < @OriginalOrderVal --Moving down chain 

--Create space for the movement; no point in changing the original 
    Update product set order = order+1 
    where order BETWEEN @NewOrderVal and @OriginalOrderVal-1;

end if

If @NewOrderVal > @OriginalOrderVal --Moving up chain

--Create space  for the momvement; no point in changing the original  
  Update product set order = order-1 
  where order between @OriginalOrderVal+1 and @NewOrderVal
end if

--Finally update the one we moved to correct value

    update product set order = @newOrderVal where ID=@IDToChange;

Regarding best practice; most environments I’ve been in typically want something grouped by category and sorted alphabetically or based on “popularity on sale” thus negating the need to provide a user defined sort.