通过窗口函数将供应商的数量与最小值和最大值进行比较，并在外部查询级别上运行条件计数：
SELECT vendor_id
, count(min_bid OR NULL) AS min_bid_count
, count(max_bid OR NULL) AS max_bid_count
FROM (
SELECT vendor_id
, amount = min(amount) OVER w AS min_bid
, amount = max(amount) OVER w AS max_bid
FROM rfq_vendor_mapping
WINDOW w AS (PARTITION BY rfq_id)
) sub
GROUP BY 1
ORDER BY 1;
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