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+```mysql
+drop database if exists a;
+create database a charset utf8;
+use a;
+create table `user` (
+	user_id int,
+	user_name varchar(20),
+	user_tel char(11),
+	ordertime date
+);
+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);
+create table `order`(
+	order_id int,
+	user_id int,
+	type varchar(20),
+	food varchar(20),
+	number int,
+	price int
+);
+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;
+-- 2.由于顾客3退单，请把此订单删除。
+delete from `order` where user_id=3;
+-- 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;
+```
+