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

Taking Tony Andrews' answer into consideration, you could alternatively store a "next" index with each entry. Then when you pull them all in, walk the array by following the chain. That makes moving an item easier, as you only have to touch maximum two rows.

The disadvantage with this approach is if you ever need a subset (e.g. the first 3 items) you still need to pull in all the items, or use a SQL loop. So it's between affecting all rows during update, or accessing all items during read. As ever, measure the speed and see which is better for your situation.