Postgres：获取多对多关系中的最小和最大行数 table

Question

我有 RFQ（询价）和供应商投标金额的映射 table。

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table中，我想分析供应商为每个 RFQ 提交了多少次最低和最高出价。

预期输出：

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

将供应商的金额与 window 函数的最小值和最大值以及运行外部查询级别的条件计数进行比较：

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.

Postgres：获取多对多关系中的最小和最大行数 table

Postgres : get min and max rows count in many to many relation table

sql

postgresql

hibernate

ejb

jpa