Question

我有三个表：产品， PC ，笔记本电脑，具有以下架构。

Product (maker, model, type)
PC (model, speed, ram, hd, price)
Laptop (model, speed, ram, hd, screen, price)

如何检索制造商A制作的所有产品的型号和价格？

我试过这个

SELECT * 
  FROM Product 
 WHERE maker = "A" 
  JOIN type.model,type.price;

和这个

SELECT * 
  FROM Product 
  JOIN Laptop ON Laptop.model;

......但没有运气。

编辑：如果我想让它更通用，我怎么能显示制造商A制造的任何产品的型号和价格，而不仅仅是笔记本电脑和PC？

Answer 1

(SELECT product.maker, laptop.model, laptop.price
 FROM Product 
 INNER JOIN laptop ON product.model = laptop.model
 WHERE product.maker = "A" )
UNION
(SELECT product.maker, pc.model, pc.price
 FROM Product 
 INNER JOIN pc ON product.model = pc.model
 WHERE product.maker = "A" )

Answer 2

SELECT model, price FROM Product INNER JOIN PC ON Product.model = PC.model WHERE maker = "A"
UNION
SELECT model, price FROM Product INNER JOIN Laptop ON Product.model = Laptop.model WHERE maker = "A"

Answer 3

有些观点：

字符串是单引号而不是双引号。
你应该考虑使用UNION ALL。
你应该将PC加入到PRODUCT和LAPTOP到PRODUCT上的模型。

这是SQL：

SELECT PC.MODEL, PC.PRICE
FROM   PC
JOIN   PRODUCT ON PRODUCT.MODEL = PC.MODEL AND PRODUCT.MAKER = 'A'
UNION ALL
SELECT LAPTOP.MODEL, LAPTOP.PRICE
FROM   LAPTOP
JOIN   PRODUCT ON PRODUCT.MODEL = LAPTOP.MODEL AND PRODUCT.MAKER = 'A'

Answer 4

看看一些mysql join tutorials，这样你就可以自己知道如何做了。

我认为product.model同时引用pc.model和laptop.model。你可能想要使用mysql IF：

这样的查询

SELECT IF(laptop.price IS NULL, pc.price, laptop.price) AS `price`, product.model
FROM product
LEFT JOIN pc ON (pc.model = product.model AND product.type = 'pc')
LEFT JOIN laptop ON (laptop.model = product.model AND product.type = 'laptop')
GROUP BY product.id
HAVING price IS NOT NULL

MySQL帮助嵌套查询和连接

4 个答案: