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+```mysql
+create database hm3 charset utf8;
+use hm3;
+create table `user`(
+user_id int,
+user_name varchar(20),
+user_tel int,
+ordertime date 
+);
+
+create table `order`(
+order_id int,
+uesr_id int,
+type varchar(20),
+food varchar(20),
+number int,
+price int
+);
+
+insert into `user` values
+(1,'张三','19865645691','2023-3-13'),
+(2,'李四','12345675691','2023-3-13'),
+(3,'王五','12895678901','2023-3-13'),
+(4,'老六','12345678691','2023-3-14'),
+(5,'小七','18945678031',null),
+(6,'老八','19345678561','2023-3-16'),
+(7,'朱九','15845679911',null);
+alter table `user` modify user_tel varchar(20);
+
+insert into `order` values
+(1,1,'快餐','肯德基全家桶',1,50),
+(2,1,'快餐','可乐',4,20),
+(3,6,'饮料','柠檬水',2,16),
+(4,2,'米饭','鱼香肉丝盖饭',5,60),
+(5,2,'饮料','珍珠奶茶',3,22),
+(6,3,'粉面类','螺蛳粉',4,28),
+(7,4,'粉面类','凉拌面',1,10);
+
+-- 1.在用户表（user）新增一个性别字段user_sex，数据类型为char。
+alter table `user` add user_sex char;
+select * from `user`;
+-- 2.由于顾客3退单，请把此订单删除。
+delete from `order` where order_id=3;
+ `order`;
+-- 3.老八的电话号码换新了，请将他的号码更新为8888888888。
+update `user` set user_tel='8888888888' where user_name='老八';
+-- 4.查询order表里的最高金额和总金额。
+select max(price),sum(price) from `order`;
+-- 5.查询每个顾客分别订购了几个类别。
+select user_name,count(type) from `user` left join (select distinct user_id,type from `order`) a on a.user_id=`user`.user_id group by user_name;
+-- 6.查询饮料的总金额
+select sum(price)*sum(number) from `order` where type='饮料';
+-- 7.查询订单表（order）里的订单号，类别（type），食物（food）.
+select order_id 订单号,type 类别,food 食物 from `order` ;
+-- 8.查询没吃饭的人的所有信息
+select `user`.* from `user` left join `order` on `order`.user_id=`user`.user_id where `order`.user_id is null;
+-- 9.查询姓老的人的全部信息及订单信息
+select * from `user` left join `order` on `order`.user_id=`user`.user_id where user_name like '老%';
+-- 10.查询总金额大于20的订单里最大值的用户信息，使用降序排列。
+select user_id 用户,sum(price)*sum(number) 总金额 from `order` group by user_id having sum(price)*sum(number)>20 order by sum(price)*sum(number) desc; 
+```
+