1、创建一张某超市的购物表，字段包括：商品名，购物价格，商品生产日期，商品分类；
CREATE TABLE menu (
id int PRIMARY KEY auto_increment,
name char(10),
price FLOAT (5,2),
product_time DATE ,
class CHAR(10)
)CHARACTER SET utf8;

向该表中插入多条数据；
INSERT INTO menu (name,price,product_time,class) VALUES
("苹果",20,20170612,"水果"),
("香蕉",80,20170602,"水果"),
("水壶",120,20161216,"电器"),
("被罩",70,20170612,"床上用品"),
("音响",420,20160216,"电器"),
("床单",55,20170612,"床上用品"),
("草莓",34,20170612,"水果");

2、查询：
(1)每一类商品花的总价格
SELECT class,sum(price) 总价格 FROM menu GROUP BY class;

(2)统计每类商品各有多少件
SELECT class,count(id) 件数 FROM menu GROUP by class;

(3)统计水果花了多少钱（两种方式实现）
SELECT class,sum(price) from menu GROUP by class HAVING class="水果";
SELECT class,sum(price) FROM menu WHERE class = "水果";

(4)统计购买的2017-01-12日生产的商品中价格最贵的商品（插入的数据中包括2017-01-12生产的商品）
SELECT name,price FROM menu where product_time<20170112 ORDER BY price desc limit 1;

(5)统计购买商品的总价格
SELECT sum(price) 购买商品总价格 FROM menu;

练习一