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+```mysql
+create database biao charset utf8;
+use biao;
+create table user(
+	user_id int primary key auto_increment,
+	user_name varchar(10),
+	user_tel varchar(11),
+	ordertime date
+);
+create table `order`(
+	order_id int primary key auto_increment,
+	user_id int,
+	type varchar(10),
+	food varchar(10),
+	number int,
+	price int,
+	foreign key (user_id) references user(user_id)
+);
+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);
+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 type from `order` group by type;
+-- 6.查询饮料的总金额
+select sum(price) 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 user_id,type,food from `order`;
+-- 8.查询没吃饭的人的所有信息
+select a.* from `user` a left join `order` b on a.user_id = b.user_id where food is null;
+-- 9.查询姓老的人的全部信息及订单信息
+select * from `user` a left join `order` b on a.user_id = b.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 a.user_id,user_name,user_tel,ordertime from `user` a left join `order` b on a.user_id = b.user_id where price > 20 order by price desc;
+```
+