1、建表

customers 顾客表

products 产品表

orders 订单表

-- 顾客表
CREATE TABLE customers (c_id INT NOT NULL AUTO_INCREMENT,lastname VARCHAR(255),firstname VARCHAR(255),address VARCHAR(255),birthday DATETIME,PRIMARY KEY (c_id)
);
-- 产品表
CREATE TABLE products (p_id INT NOT NULL AUTO_INCREMENT,productname VARCHAR(255),price FLOAT(12 , 3 ), -- 写 3 是为了等一下试一下 round 函数stock INT,PRIMARY KEY (p_id)
);
-- 订单表
CREATE TABLE orders (o_id INT NOT NULL AUTO_INCREMENT,c_id INT,p_id INT,quantity INT,create_time DATETIME,PRIMARY KEY (o_id),-- 曾经有前辈和我说，在 Mysql 中外键约束不适合在高并发情况下使用，容易死锁，这里只是练习FOREIGN KEY (c_id) REFERENCES customers (c_id),FOREIGN KEY (p_id)REFERENCES products (p_id)
);

2、增加数据

-- Add some data to customers
insert into customers values (null, '三', '张', '上海市黄浦区', '1988-09-29 18:20:18');
insert into customers values (null, '四', '李', '上海市静安区', '1992-01-15 19:17:55');
insert into customers values (null, '无', '钱', '上海市浦东新区', '1982-07-25 05:21:37');
insert into customers values (null, '吴', '周', '上海市虹口区', '1995-02-18 12:30:09');
insert into customers values (null, '王', '郑', '上海市徐汇区', '1999-01-19 11:45:18');
-- Just select 
SELECT *
FROMcustomers;
-- Add some data to products 
insert into products values (null, '无线路由器', 110.091, 100);
insert into products values (null, '雷蛇鼠标', 320.50, 200);
insert into products values (null, 'cherry 键盘', 600.1, 300);
insert into products values (null, 'AOG 显示器', 1100.0, 400);
insert into products values (null, '甜筒', 3, 500);
-- Just select
SELECT *
FROMproducts;
-- Let buy some products for add data to orders
insert into orders values (null, 1, 1, 1, date_sub(now(),interval 1 day));
insert into orders values (null, 1, 2, 2, date_sub(now(),interval 1 day));
insert into orders values (null, 1, 3, 3, date_sub(now(),interval 2 day));
insert into orders values (null, 1, 4, 4, date_sub(now(),interval 2 day));
insert into orders values (null, 2, 5, 7, date_sub(now(),interval 5 hour));
insert into orders values (null, 3, 2, 1, date_sub(now(),interval 5 hour));
insert into orders values (null, 4, 4, 2, now());
insert into orders values (null, 4, 5, 2, now());
-- Just select
SELECT *
FROMorders;

3、做统计

（1）当天 雷蛇鼠标的销售额

-- 当天 雷蛇鼠标的销售额
SELECT SUM(o.quantity) AS router_sales_quantity
FROMorders oLEFT JOINproducts p ON o.p_id = p.p_id
WHEREp.productname = '雷蛇鼠标'AND DATE(o.create_time) = DATE(NOW());

（2）雷蛇鼠标 在 80 后人群中的销售额

-- 雷蛇鼠标 在 80 后人群中的销售额
SELECT round(sum(o.quantity * p.price), 2) as productname_sum_money
FROMorders oLEFT JOINproducts p ON o.p_id = p.p_idLEFT JOINcustomers c ON o.c_id = c.c_id
WHEREp.productname = '雷蛇鼠标'AND EXTRACT(YEAR FROM c.birthday) BETWEEN '1980' AND '1990';

（3）80 , 90 后人群的总销售额和平均销售额

-- 80 , 90 后人群的总销售额和平均销售额
SELECT CASEWHENEXTRACT(YEAR FROM c.birthday) >= '1980'AND EXTRACT(YEAR FROM c.birthday) < '1990'THEN'80'WHENEXTRACT(YEAR FROM c.birthday) >= '1990'AND EXTRACT(YEAR FROM c.birthday) < '2000'THEN'90'ELSE 'null'END AS age,ROUND(SUM(o.quantity * p.price), 2) AS sum_money,ROUND(AVG(o.quantity * p.price), 2) AS avg_money
FROMorders oLEFT JOINproducts p ON o.p_id = p.p_idLEFT JOINcustomers c ON o.c_id = c.c_id
GROUP BY age;

...

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