Top 3 Items Per Region Query

The Apexon Data & AI platform tracks high-volume user transactions across regions. Write a PostgreSQL query that identifies the three most purchased items in each region during the last 30 days, using completed transactions only.

Output

1. Return one row per item included in the regional top three, with columns region, item_id, item_name, purchased_units, and region_rank.
2. Exclude transactions outside the inclusive 30-day interval ending on 2026-08-29, transactions that are not completed, transactions with non-positive or NULL quantities, and users whose region is NULL.
3. Aggregate purchased units by region and item, rank items independently within each region, and return no more than three rows per region.
4. Break quantity ties by ascending item_id, and order the final result by region and region_rank.