Time complexity of Cursor Pagination

Question

I have read from different articles saying cursor pagination query has time complexity O(1) or O(limit) where limit is the number of item limit in sql. Some example article source: https://uxdesign.cc/why-facebook-says-cursor-pagination-is-the-greatest-d6b98d86b6c0 and https://dev.to/jackmarchant/offset-and-cursor-pagination-explained-b89

But I canont find related references explaining why the time complexity is O(limit). Say I have a table consist of 3 columns id, name, created_at, where id is primary key,

if I use created_at as the cursor (which is unique and sequential), can someone explain why the time complexity is O(limit)？

Is it related to data structure used to store created_at?

Answer 1

After some reading, I guess the time complexity is talking about after retrieving the intermediate records, the time complexity of getting the final required records.

For offset case, all records will be selected, then database will discard x records where x is the offset, finally select y records (where y = limit), so the time complexity is O(offset + limit).

For cursor case, records matched the cursor where condition will be selected, then select y records (where y = limit), so the time complexity is O(limit).