Question

我有一个包含表格的数据库：

suppliers:
 fid , name
   1 | 'Andrey' 
   2 | 'lucas'

products:
 pid , name
   1 | 'X' 
   2 | 'Y' 

prdtFrn:
 pid , fid , price
  ---------------- supplier 'andrey'
   1 |  1  | 19.00 
   2 |  1  | 16.00 
  ----------------- supplier 'lucas'
   1 |  2  | 14.00 
   2 |  2  | 18.00

查询产品，我得到所有已注册的产品，但我需要知道谁以“最低价”销售“产品表”的当前产品，我不知道如何编写查询

Answer 1

select p.* 
from (
    select pid, min(price) as MinPrice
    from prdtFrn
    group by pid
) pm
inner join prdtFrn p on pm.pid = p.pid and pm.MinPrice = p.price

每个产品会看到多个行，其中两个供应商以相同的价格销售产品。

Answer 2

与任何复杂的SQL一样，逐步构建它。

SELECT s.name AS s_name, p.name AS p_name, sp.price
  FROM suppliers AS s
  JOIN prdtFrn   AS sp ON s.fid = sp.fid
  JOIN products  AS p  ON p.pid = sp.pid

这将为您提供卖家，产品和价格的清单。现在，据推测，对于每种产品，您都需要以最小价格销售产品的供应商名称的详细信息：

SELECT p_name, MIN(price) AS min_price
  FROM (SELECT s.name AS s_name, p.name AS p_name, sp.price
          FROM suppliers AS s
          JOIN prdtFrn   AS sp ON s.fid = sp.fid
          JOIN products  AS p  ON p.pid = sp.pid
       ) AS spp

这为您提供每种产品的最低价格。现在，您需要将结果与第一个查询相结合，以得出答案：

SELECT spp.p_name, spp.s_name, min_price
  FROM (SELECT s.name AS s_name, p.name AS p_name, sp.price
          FROM suppliers AS s
          JOIN prdtFrn   AS sp ON s.fid = sp.fid
          JOIN products  AS p  ON p.pid = sp.pid
       ) AS spp
  JOIN (SELECT p_name, MIN(price) AS min_price
          FROM (SELECT s.name AS s_name, p.name AS p_name, sp.price
                  FROM suppliers AS s
                  JOIN prdtFrn   AS sp ON s.fid = sp.fid
                  JOIN products  AS p  ON p.pid = sp.pid
               ) AS spp
       ) AS mp
    ON mp.p_name = spp.p_name AND mp.min_price = spp.price;

然后，当它工作时，您可以优化...例如，最低价格计算不需要供应商信息：

SELECT spp.p_name, spp.s_name, mp.min_price
  FROM suppliers AS s
  JOIN prdtFrn   AS sp ON s.fid = sp.fid
  JOIN (SELECT pid, MIN(price) AS min_price
          FROM prdtFrn
         GROUP BY pid
       ) AS mp
    ON mp.pid = sp.pid AND mp.min_price = sp.price;

我的第一个查询出错了，因为我提供了比第一个查询中所需的更多信息;这更简单。所以，这里的课程是：

逐个构建查询。
对初稿不满意。

谁以最低价出售

2 个答案: