Get the Latest Entry for Each Group Using Window Functions

WITH RankedItems AS (
  SELECT
    item_id,
    group_id,
    value,
    created_at,
    ROW_NUMBER() OVER(PARTITION BY group_id ORDER BY created_at DESC) as rn
  FROM items
)
SELECT item_id, group_id, value, created_at
FROM RankedItems
WHERE rn = 1;

How it works: This snippet uses a Common Table Expression (CTE) and the `ROW_NUMBER()` window function to find the latest record within each group. `PARTITION BY group_id` divides the data into groups based on the `group_id`, and `ORDER BY created_at DESC` assigns a rank within each group, with the most recent item getting rank 1. The outer query then filters for `rn = 1` to select only the latest item from each group.