VIP(상위20%) 매출 기여도

WITH u AS (
  SELECT o.user_id, SUM(i.price * o.quantity) AS gmv
  FROM orders o
  JOIN items  i ON i.item_id = o.item_id
  WHERE o.status = 'completed'
  GROUP BY o.user_id
),
tiled AS (
  SELECT user_id, gmv,
         NTILE(5) OVER(ORDER BY gmv DESC) AS tile5
  FROM u
)
SELECT
  ROUND(SUM(CASE WHEN tile5=1 THEN gmv ELSE 0 END) / NULLIF(SUM(gmv),0) * 100, 2)
    AS top20_share_pct
FROM tiled;