在mysql中使用IN和UNION无法正确形成数据集

Question

数据库架构

问题 -

  

找出所有产品（任何类型）的型号和价格   由制造商B制作。

我的尝试 -

SELECT b.model, b.price FROM laptop AS b 
WHERE b.model IN ( SELECT model FROM product WHERE maker = 'B')
UNION
SELECT c.model, c.price FROM pc AS c 
WHERE c.model IN ( SELECT model FROM product WHERE maker = 'B')
UNION
SELECT d.model, d.price FROM printer AS d 
WHERE d.model IN ( SELECT model FROM product WHERE maker = 'B')

即使这没有显示只有B的正确数据集 -

SELECT b.model, b.price FROM laptop AS b 
WHERE b.model IN ( SELECT model FROM product WHERE maker = 'B')

只有一个结果集即将到来。

让我知道使用查询进行的逻辑错误。

编辑 -

输出 -

SELECT model FROM product WHERE maker = 'B'

SELECT b.model, b.price FROM laptop AS b 
WHERE b.model IN ( SELECT model FROM product WHERE maker = 'B')

查询 - SELECT * FROM product WHERE maker = 'B'

输出 -

Answer 1

SELECT b.model, b.price FROM laptop AS b 
...
SELECT c.model, c.price FROM laptop AS c 
...
SELECT d.model, d.price FROM laptop AS d 

您从笔记本电脑中选择3次，结果相同。然后你UNION将它们放在一起，这将删除所有重复项。

编辑：您的示例查询;

SELECT b.model, b.price FROM laptop AS b 
WHERE b.model IN ( SELECT model FROM product WHERE maker = 'B')

只会找到笔记本电脑，因为这是唯一使用过的表格。 1121是PC，因此查询不会显示它。