Storing item positions (for ordering) in a database efficiently

Question

Scenario:

There is a database of movies a user owns, movies are displayed on a page called \"my-movies\", the movies can be displayed in the order that the user desires.

Answer 1

Store the order linked-list style. Instead of saving the absolute position, save the ID of the previous item. That way any change only requires you to update two rows.

movieid | userid  | previousid
   1    |    1    | 
   2    |    1    |    1
   3    |    1    |    4
   4    |    1    |    2

To get the movies in order ...

SELECT movieid WHERE userid = 1 ORDER BY previousid

-> 1, 2, 4, 3

To (say) move #4 up a space:

DECLARE @previousid int, @currentid int
SET @previousid = SELECT previousid FROM movies WHERE movieid = @currentid

-- current movie's previous becomes its preceding's preceding
UPDATE movies SET previousid = 
    (SELECT previousid FROM movies WHERE movieid = @previousid)
WHERE movieid = @currentid

-- the preceding movie's previous becomes the current one's previous
UPDATE movies SET previousid = @currentid WHERE movieid = @previousid

That's still 1 read + 2 writes, but it beats 10,000 writes.