这个查询的错误在哪里？ （sql-ex.ru 练习 25）

Question

我正在尝试从 sql-ex.ru 解决练习 25 ：

数据库方案由四个表组成：

• 产品（制造商、型号、类型）
• PC（代码、型号、速度、内存、高清、CD、价格）
• 笔记本电脑（代码、型号、速度、内存、高清、屏幕、价格）
• 打印机（代码、型号、颜色、类型、价格）

在所有具有最低 RAM 容量的 PC 中，查找还生产具有最低 RAM 容量和最高处理器速度的 PC 的打印机制造商。 结果集：制造商。

我不明白为什么以下查询不会在第二个检查数据库上产生所需的结果：

SELECT DISTINCT product.maker
FROM product
RIGHT JOIN printer ON printer.model = product.model
WHERE product.maker IN(
    SELECT product.maker
    FROM product
    RIGHT JOIN pc ON pc.model = product.model
    WHERE pc.ram = (SELECT MIN(ram) FROM pc)
    AND pc.speed = (
        SELECT MAX(t.speed)
        FROM (SELECT speed FROM pc WHERE ram = (SELECT MIN(ram) FROM pc)) AS t
    )
)

错误如下：

Wrong
Your query produced correct result set on main database, but it failed test on second, checking database
* Wrong number of records (less by 1)

为什么它不能准确地选择 1 个制造商？

Answer 1

我不知道您的查询中的错误在哪里，但您可以使用以下内容：

WITH t AS ( SELECT * FROM PC c WHERE c.ram = (SELECT MIN(ram) FROM PC) ) SELECT DISTINCT a.maker FROM Product a WHERE a.type = 'PC' AND a.maker IN ( SELECT b.maker FROM Product b WHERE b.type = 'Printer' ) AND a.model IN ( SELECT model FROM t WHERE speed = (SELECT MAX(speed) FROM t) ) 

Answer 2

下面是这个问题的解决方案：

WITH CTE_Product AS
(
    SELECT DISTINCT
        Maker
    FROM
        Product
    WHERE
        Type = 'PC'
    AND
        Maker IN (SELECT Maker FROM Product WHERE Type = 'Printer')
)

select c.maker from CTE_Product C
inner join
(
select distinct maker from product inner join PC on product.model=pc.model 
where type='PC'and  
pc.speed in 
          (select max(speed) 
           from pc 
           where ram=
                     (select min(ram)from pc)
           )
 and pc.ram=
             (select min(ram)
              from pc)
) A on A.maker = C.maker

Answer 3

SELECT DISTINCT maker
  FROM Product
 WHERE TYPE = 'Printer'

 INTERSECT

SELECT DISTINCT maker
  FROM Product AS p
    INNER JOIN PC as pc
    ON p.model = pc.model
    WHERE
      type = 'PC'
      AND (pc.ram = ALL (SELECT MIN(ram) FROM PC))
        AND (pc.speed = (SELECT MAX(speed) FROM PC WHERE ram = (SELECT MIN(ram) FROM PC )))