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+```mysql
+CREATE DATABASE food charset utf8;
+use food;
+CREATE TABLE `user` (
+user_id int,
+user_name VARCHAR(20),
+user_tel VARCHAR(20),
+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(10),
+food VARCHAR(10),
+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);
+
+-- 根据上表所给信息完成下列题目：
+
+-- 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 COUNT(type) FROM `order`;
+-- 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 order_id,type,food FROM `order`;
+-- 8.查询没吃饭的人的所有信息    
+   SELECT `user`.*,order_id,type,food,number,price FROM `user` LEFT JOIN `order` ON `user`.user_id=`order`.user_id WHERE order_id is null;
+-- 9.查询姓老的人的全部信息及订单信息
+   SELECT * FROM `user` 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。GROUP BY u.user_id
+	 select * from `order` o left join user u on o.user_id=u.user_id  HAVING price>20 order by price desc;
+```
+
+
+