How to save a particular, mutable “order” into a database

Question

Suppose I have some objects, and I want the user to be able to reorder them in any way they wish, say, by dragging them around. So I\'d have

• Cheese
• Muffin

Answer 1

Theoretically you could use an Order Statistic Tree if you want to get a specific element at a value, or just some kind of B-Tree in general to store the values. If they change, you are changing O(log n) items in the worst case. If you have 30,000 items, you only need to change 4 or 5 or them to keep the order.