## The situation
Suppose there is a big dataset (say 200,000 items).
Each item requires a specified unique rank (from 1 to 200,000)
Need to update some item's rank frequently.
## Temporary solution and problem
Store all items in a table:
```sqlite
CREATE TABLE dataset (
id INTEGER PRIMARY KEY,
item TEXT
);
```
Each row stores one item, and make the `id` as it's rank.
But when updating one item's rank, say from `m` to `n`, I need to alter all the `id`s between 'm' and `n`. The time complexity is O(m-n).
Say the m is 100000 and the n is 100, then updating one item's rand requires updating 99900 `id`s, making that kind of rank update 1000 times requires updating 99900000 `id`s. That is insane.
Is there a more efficient way to organize this kind of dataset?
- Each item requires a specified unique and continuous rank, which can be used for ordering.
- The item's rank often need to update.