1、建表

customers 顧客表

products 產品表

orders 訂單表

-- 顧客表
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)
);
-- 產品表
CREATE TABLE products (p_id INT NOT NULL AUTO_INCREMENT,productname VARCHAR(255),price FLOAT(12 , 3 ), -- 寫 3 是為了等一下試一下 round 函數stock INT,PRIMARY KEY (p_id)
);
-- 訂單表
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),-- 曾經有前輩和我說，在 Mysql 中外鍵約束不適合在高并發情況下使用，容易死鎖，這里只是練習FOREIGN KEY (c_id) REFERENCES customers (c_id),FOREIGN KEY (p_id)REFERENCES products (p_id)
);

2、增加數據

-- Add some data to customers
insert into customers values (null, '三', '張', '上海市黃浦區', '1988-09-29 18:20:18');
insert into customers values (null, '四', '李', '上海市靜安區', '1992-01-15 19:17:55');
insert into customers values (null, '無', '錢', '上海市浦東新區', '1982-07-25 05:21:37');
insert into customers values (null, '吳', '周', '上海市虹口區', '1995-02-18 12:30:09');
insert into customers values (null, '王', '鄭', '上海市徐匯區', '1999-01-19 11:45:18');
-- Just select 
SELECT *
FROMcustomers;
-- Add some data to products 
insert into products values (null, '無線路由器', 110.091, 100);
insert into products values (null, '雷蛇鼠標', 320.50, 200);
insert into products values (null, 'cherry 鍵盤', 600.1, 300);
insert into products values (null, 'AOG 顯示器', 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、做統計

（1）當天 雷蛇鼠標的銷售額

-- 當天 雷蛇鼠標的銷售額
SELECT SUM(o.quantity) AS router_sales_quantity
FROMorders oLEFT JOINproducts p ON o.p_id = p.p_id
WHEREp.productname = '雷蛇鼠標'AND DATE(o.create_time) = DATE(NOW());

（2）雷蛇鼠標 在 80 后人群中的銷售額

-- 雷蛇鼠標 在 80 后人群中的銷售額
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 = '雷蛇鼠標'AND EXTRACT(YEAR FROM c.birthday) BETWEEN '1980' AND '1990';

（3）80 , 90 后人群的總銷售額和平均銷售額

-- 80 , 90 后人群的總銷售額和平均銷售額
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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