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+| 用户表（user）  |           |             |              |        |       |
+| --------------- | --------- | ----------- | ------------ | ------ | ----- |
+| user_id         | user_name | user_tel    | ordertime    |        |       |
+| 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 |              |        |       |
+| 6               | 老八      | 19345678561 | 2023-3-16    |        |       |
+| 7               | 朱九      | 15845679911 |              |        |       |
+| 订单表（order） |           |             |              |        |       |
+| order_id        | uesr_id   | type        | food         | number | price |
+| 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    |
+
+建表
+
+```mysql
+CREATE DATABASE wmm CHARSET utf8;
+use wmm;
+CREATE TABLE `user`(
+user_id INT,
+user_name VARCHAR(20),
+user_tel VARCHAR(20),
+ordertime DATE
+);
+
+CREATE TABLE `order`(
+order_id INT,
+user_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');
+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。
+
+```mysql
+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。
+
+```mysql
+SELECT *FROM `user` a LEFT JOIN `order` b on a.user_id = b.user_id;
+```
+
+-- 6.查询饮料的总金额
+
+```mysql
+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）.
+
+```mysql
+SELECT type,food FROM `order` GROUP BY type='food';
+```
+
+-- 8.查询没吃饭的人的所有信息
+
+```mysql
+SELECT *FROM `user` a LEFT JOIN `order` b on a.user_id = b.user_id WHERE b.user_id is NULL;
+```
+
+-- 9.查询姓老的人的全部信息及订单信息
+
+```mysql
+SELECT *FROM `user` a LEFT JOIN `order` b on a.user_id = b.user_id WHERE a.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。
+
+```mysql
+SELECT a.* FROM `user` a LEFT JOIN `order` b on a.user_id = b.user_id WHERE b.price >20 ORDER BY price DESC;
+```
+