Kas teate partition kontseptsioonist ja kuidas kasutatakse PARTITION BY koos ORDER BY-ga?

The concept of partitions in SQL is used to divide a dataset into logical groups, over which window functions can be applied. The keyword PARTITION BY determines how to split the data into these groups.

ORDER BY inside the window function sets the order of rows within each partition, which is important for functions that depend on order, such as ROW_NUMBER(), LAG(), LEAD(), etc.

Example:

SELECT
  user_id,
  event_time,
  ROW_NUMBER() OVER (PARTITION BY user_id ORDER BY event_time) AS event_rank
FROM events;

Here, data for each user (user_id) is divided into partitions, and within each partition, events are sorted by time to number them in chronological order.