Postgres：在多對多關係表中獲取最小和最大行數

Question

我有RFQ（報價請求）和供應商出價金額的映射表。

rfq_vendor_mapping：

id rfq_id(FK) vendor_id(FK) amount 
--------------------------------------- 

1  1   1   100 
2  1   2   50 
3  2   1   200 
4  2   3   300 
5  2   2   40 
6  3   4   70 
7  3   1   90 
8  3   2   250 
9  4   3   30 
10  5   1   500 

在上面的表格，我要如何廠商多次提交最低和最高出價爲每RFQ分析。

預期輸出：

vendor_id min_bid_count max_bid_count 
----------------------------------------- 
    1   1    2 
    2   2    1 
    3   1    2 
    4   1    0 

http://sqlfiddle.com/#!15/60198/1

Answer 1

從一個窗口函數比較供應商的與最小和最大金額和外部查詢級別運行條件計數：

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; 

SQL Fiddle.