表结构

本文使用的表结构如下：

以下是创建表的语句：

-- 厂商表
CREATE TABLE Manufacturers (
  Code INTEGER NOT NULL PRIMARY KEY, -- 编号，主键
  Name VARCHAR(255) NOT NULL, -- 名称
);

-- 产品表
CREATE TABLE Products (
  Code INTEGER NOT NULL PRIMARY KEY, -- 编号，主键
  Name VARCHAR(255) NOT NULL, -- 名称
  Price DECIMAL NOT NULL, -- 价格
  Manufacturer INTEGER NOT NULL, -- 厂商编号
  FOREIGN KEY (Manufacturer) REFERENCES Manufacturers(Code) -- 外键，引用厂商表
);

-- 测试数据
INSERT INTO Manufacturers(Code,Name) 
VALUES (1,'Sony'),
       (2,'Creative Labs'),
       (3,'Hewlett-Packard'),
       (4,'Iomega'),
       (5,'Fujitsu'),
       (6,'Winchester');

INSERT INTO Products(Code,Name,Price,Manufacturer) 
VALUES (1,'Hard drive',240,5),
       (2,'Memory',120,6),
       (3,'ZIP drive',150,4),
       (4,'Floppy disk',5,6),
       (5,'Monitor',240,1),
       (6,'DVD drive',180,2),
       (7,'CD drive',90,2),
       (8,'Printer',270,3),
       (9,'Toner cartridge',66,3),
       (10,'DVD burner',180,2);

练习题

查看全部产品的名称

SELECT Name FROM Products;

查看全部产品的名称和价格

SELECT Name, Price FROM Products;

查看价格小于等于 200 的产品名称

SELECT Name FROM Products WHERE Price <= 200;

查看价格位于 60 到 120 之间的产品

/* 使用 AND 运算符*/
SELECT * FROM Products
WHERE Price >= 60 AND Price <= 120;
 
/* 使用 BETWEEN 运算符*/
SELECT * FROM Products
WHERE Price BETWEEN 60 AND 120;

查看全部产品的名称和价格，价格以分为单位显示

SELECT Name, Price * 100 AS PriceCents FROM Products;

计算全部产品的平均价格

SELECT AVG(Price) FROM Products;

计算厂商编号为 2 的所有产品的平均价格

SELECT AVG(Price) FROM Products WHERE Manufacturer=2;

统计价格大于等于 180 的产品数量

SELECT COUNT(*) FROM Products WHERE Price >= 180;

查看价格大于等于 180 的产品名称和价格，按照价格降序、名称升序排序

SELECT Name, Price 
FROM Products
WHERE Price >= 180
ORDER BY Price DESC, Name;

查看全部产品以及它们的厂商信息

SELECT * FROM Products, Manufacturers
WHERE Products.Manufacturer = Manufacturers.Code;

查看全部产品的名称、价格以及厂商的名称

SELECT Products.Name, Price, Manufacturers.Name
FROM Products 
JOIN Manufacturers
ON Products.Manufacturer = Manufacturers.Code;

统计每个厂商的平均产品价格，显示厂商编号

SELECT AVG(Price), Manufacturer
FROM Products
GROUP BY Manufacturer;

统计每个厂商的平均产品价格，显示厂商名称

SELECT AVG(Price), Manufacturers.Name
FROM Products 
JOIN Manufacturers
ON Products.Manufacturer = Manufacturers.Code
GROUP BY Manufacturers.Name;

查看平均产品价格大于等于 150 的厂商名称

SELECT AVG(Price), Manufacturers.Name
FROM Products 
JOIN Manufacturers
ON Products.Manufacturer = Manufacturers.Code
GROUP BY Manufacturers.Name
HAVING AVG(Price) >= 150;

查看最便宜的产品名称和价格

SELECT Name, Price
FROM Products
ORDER BY price ASC
LIMIT 1;

/* 如果存在多个最便宜的产品，嵌套子查询可以返回多条记录 */
SELECT Name, Price
FROM Products
WHERE Price = (SELECT MIN(Price) FROM Products);

查看每个厂商及其最昂贵的产品名称和价格

SELECT A.Name, A.Price, F.Name
FROM Products A 
JOIN Manufacturers F
ON A.Manufacturer = F.Code
AND A.Price =
     (
       SELECT MAX(A.Price)
       FROM Products A
       WHERE A.Manufacturer = F.Code
     );

查看平均产品价格大于 145 并且至少生产 2 种产品的厂商名称

SELECT m.Name, Avg(p.price) AS p_price, COUNT(p.Manufacturer) AS m_count
FROM Manufacturers m, Products p
WHERE p.Manufacturer = m.code
GROUP BY m.Name
HAVING Avg(p.price) >= 150 AND COUNT(p.Manufacturer) >= 2;

增加一个新的产品

新产品的信息如下：名称为 Loudspeakers，价格为 70，厂商编号为 2。

 INSERT INTO Products( Code, Name , Price , Manufacturer)
  VALUES ( 11, 'Loudspeakers' , 70 , 2 );

将编号为 8 的产品更名为“Laser Printer”

UPDATE Products
SET Name = 'Laser Printer'
WHERE Code = 8;

将全部产品打九折

UPDATE Products
SET Price = Price - (Price * 0.1);

将价格大于等于 120 的产品打九折

UPDATE Products
SET Price = Price - (Price * 0.1)
WHERE Price >= 120;