mysql - mysql 中的 IN 和 UNION 数据集未正确形成

Question

数据库架构

问题-

Find out the models and prices for all the products (of any type) produced by maker B.

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')

即使这也没有显示仅包含 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')

仅出现一个结果集。

让我知道我在查询中犯的逻辑错误。

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 产品 WHEREmaker = '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 

您从笔记本电脑中进行了 3 次选择，结果集相同。然后将它们UNION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，因为这是唯一使用的 table 。 1121是PC，所以查询不会显示它。