Your strings could get REALLY long.

Suppose you have 3 items:

    id  pos  name
    1   'a'  apple
    2   'm'  banana
    3   'z'  cherry

You move cherry to the middle of the list. Now, you have:

    id  pos  name
    1   'a'  apple
    3   'g'  cherry
    2   'm'  banana

Now you move banana back to the middle of the list, which gives you this:

    id  pos  name
    1   'a'  apple
    2   'd'  banana
    3   'g'  cherry

Keep doing this, and the gap keeps shrinking. You need to make pos longer to be more precise to fit in the gap. Eventually you run out of space in your string field.