1.创建数据库company，在库中创建两个表offices和employees表

CREATE DATABASE company;

CREATE TABLE offices
(
 officeCode INT(10) PRIMARY KEY AUTO_INCREMENT, #主键从功能上看相当于非空且唯一所以定义为主键即不用再定义非空和唯一
 city VARCHAR(50) NOT NULL,
 address VARCHAR(50),
 country VARCHAR(50) NOT NULL,
 postalCode VARCHAR(15) UNICODE
);

CREATE TABLE employees
(
 employeeNumber INT(11) NOT NULL PRIMARY KEY AUTO_INCREMENT,
 lastName VARCHAR(50) NOT NULL,
 firstName VARCHAR(50) NOT NULL,
 mobile VARCHAR(50) UNICODE,
 officeCode INT(10) NOT NULL ,
 jobTitle VARCHAR(50) NOT NULL,
 birth DATETIME NOT NULL,
 note VARCHAR(255),
 sex VARCHAR(5),
 CONSTRAINT office_fk FOREIGN KEY(officeCode) REFERENCES offices(officeCode)
);

#2.查看该库底下几个表以及查看两张表结构
SHOW TABLES FROM company;

SHOW COLUMNS FROM offices;

SHOW COLUMNS FROM employees;

#3.将表employees的moblie字段修改到officeCode字段后面

ALTER TABLE employees MODIFY mobile VARCHAR(50) AFTER officeCode;

#4.将表employees的birth字段改名为employees_birth
ALTER TABLE employees CHANGE birth employees_birth DATETIME;

 #5.修改sex字段，数据类型为CHAR(1)，非空约束
ALTER TABLE employees MODIFY sex CHAR(1) NOT NULL;

 #6.删除字段note
ALTER TABLE employees DROP note;

 #7.增加字段名favoriate_acticity,数据类型为VARCHAR(100)
ALTER TABLE employees ADD favoriate_acticity VARCHAR(100);

 #8.删除表offices
DROP TABLE offices;

删除数据表offices；

需要注意的是数据表offices中存在着外键，所以我们删除该数据表的时候，需要先删除外键关系，然后再删除这个数据表方可。

#9.将表employees名称修改为employees_info
ALTER TABLE employees RENAME employees_info;