설치·접속: PostgreSQL 설치와 접속부제: 고객별로 "가장 최근 주문 1건"만 골라 대시보드에 노출할 때SELECT DISTINCT ON (user_id) user_id, ordered_at, totalFROM ordersORDER BY user_id, ordered_at DESC; user_id | ordered_at | total ---------+---------------------+-------- 1 | 2026-02-10 20:00:00 | 224.94 2 | 2026-02-17 13:00:00 | 353.75 3 | 2026-02-18 03:00:00 | 149.96 4 | 2026-02-19 00:00:00 | 176.91..