我的 SQL 查询中的子查询错误

Question

https://screenshot.googleplex.com/j4igYFL9sjH 在所有具有最低 RAM 容量的 PC 中，查找同时生产具有最低 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。

我的查询：

SELECT maker FROM Product WHERE type ='Printer' AND model IN(SELECT DISTINCT(model), hd, ram FROM PC 
                        WHERE hd = (
                                SELECT MAX(hd) FROM PC 
                                     WHERE model IN(SELECT DISTINCT(model) FROM PC
                                                                       WHERE ram <=(SELECT MIN(ram) FROM PC))));

原来这里没有制造商列表。我认为子查询有问题。

Answer 1

我真的不喜欢这个问题，因为它的措辞很含糊。希望这可以避免其他人为我刚刚弄清楚所问的内容而感到头疼：

SELECT DISTINCT maker FROM Product WHERE type = 'printer' AND maker IN 
  ( SELECT maker FROM Product WHERE model IN ( 
       SELECT model FROM Pc 
          WHERE ram = (SELECT MIN(ram) FROM PC)   
          AND speed = (SELECT MAX( speed) FROM 
             (SELECT speed FROM Pc WHERE 
                 ram = (SELECT MIN(ram) FROM Pc)) as z4) 
             )
  )

Answer 2

问题

1. 不能保证具有给定类别的 PC maker 也会生产打印机。当前查询不会预料到这一点，因此它可能会返回注意

2. 当前子查询不足以解决该问题，整个查询不起作用，因为子查询返回model 的 PC 具有最小 RAM、最大处理器、最大硬盘等等，然后是那个模型与product..中的所有打印机的model相比，它永远不会找到任何匹配..

解决方案

1. 翻转查询使主查询变为子查询，反之亦然，因此子查询是关于获取所有打印机maker
2. 一旦翻转，获得任何条件的PC打印机maker都很容易，只需使用order by..

守则

下面的代码返回一台打印机maker，它也使PC 具有最大的hd 和最小的ram

SELECT maker FROM product A INNER JOIN PC B ON A.model = B.model 
WHERE maker IN (SELECT DISTINCT maker FROM product WHERE type = 'printer')
ORDER BY hd DESC, ram ASC
LIMIT 1

Answer 3

这是我的回答，希望对你有帮助

SELECT distinct maker FROM product WHERE type = 'printer'
AND maker IN (SELECT maker
FROM product JOIN ( 
SELECT model, speed, ram FROM pc WHERE speed =
                (SELECT MAX(speed) FROM pc
                WHERE ram = (SELECT MIN(ram) FROM pc)
                ) 
            AND ram = (SELECT MIN(ram) FROM pc)
            ) b
ON product.model = b.model)

通过使用：

SELECT model, speed, ram FROM pc WHERE speed = 
(SELECT MAX(speed) FROM pc 
WHERE ram = (SELECT MIN(ram) FROM pc)) 

你确定它会以 100 的速度返回任何东西。 假设您有模型 1、2、3，它们的速度都是 100，但它们的 ram 不同，它将返回所有三个模型，而实际上只有模型 1 具有最低的 ram。所以你想添加

AND ram = (SELECT MIN(ram) FROM pc)

作为附加条件，以确保您在使用 pc 标准取模型时对 ram 的要求不会消失。

Answer 4

select distinct maker
from product
where 
 model in (
select model 
from  (select * from pc where ram in (select min (ram) from pc)) as A
where speed in 

(select max(speed) from
          (select * from pc  where ram in (select min(ram) from pc ))      as B)
)
and maker in (select maker  from product where type like 'printer')

Answer 5

我使用了分而治之的方法

WITH pc_lowest_ram as (
  SELECT DISTINCT model, pc.ram FROM pc
  WHERE pc.ram = (
   SELECT MIN(ram) FROM PC
  )
),
printer_makers AS (
  SELECT DISTINCT maker FROM product p
  WHERE p.type = 'Printer'
),
pc_max_speed AS (
  SELECT MAX(speed) pm FROM pc
  JOIN pc_lowest_ram plr on (plr.model = pc.model)
  WHERE plr.ram = pc.ram
),
pc_models AS (
  SELECT pc.model pm FROM pc
  JOIN pc_lowest_ram plr on (plr.model = pc.model)
  WHERE plr.ram = pc.ram
  AND pc.speed = (
    SELECT pm FROM pc_max_speed
  )
)
SELECT DISTINCT p.maker FROM product p
JOIN printer_makers ON (printer_makers.maker = p.maker)
JOIN pc_models ON (pc_models.pm = p.model)