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+```mysql
+#第一题
+
+create datebase test01_market charset utf8;
+use test01_market;
+create table customers(
+c_unm int(11),
+c_name varchar(50),
+c_contact varchar(50),
+c_city varchar(50),
+c_birth date
+);
+alter table customers modify c_contact varchar(50) after c_birth;
+alter table customers modify c_name varchar(70);
+alter table customers change c_contact c_phone varchar (50);
+alter table customers add c_gender int not null after `c_name`;
+alter table customers modify c_gender char(1);
+rename table customers to customers_info;
+alter table customers drop c_city;
+```
+
+
+
+```mysql
+#第二题
+
+
+creast datebase test02_library charset uft8;
+use test02_library;
+create table books(
+b_id int(11) not null comment '书编号',
+b_name varchar(50) not null comment '书名',
+`authors` varchar(100) not null comment '作者',
+price float(2,1) not null comment '价格',
+pubdate year not null comment '出版日期',
+note varchar(100) comment '说明',
+num int (11) not null comment '库存'
+);
+desc books;
+insert into books values(1,'Tal of AAA','Dickes',23.0,1995,'nove',11);
+insert into books values(2,'EmmaT','Jane lura',35.0,1993,'joke',22);
+insert into books values(3,'Story of jane','Jane Tim',40.0,2001,'novel',0);
+insert into books values(4,'Love Day','George Byron',20.0,2005,'nove;',30);
+insert into books values(5,'Old land ','Honore Blade',30.0,2010,'law',0);
+insert into books values(6,'The Battle','Upton Sara',30.0,1999,'medicine',40);
+insert into books values(7,'Rose Hood','Richad haggard',28.0,2008,'cartoon',28);
+update books set price=price+5;
+update books set price=40 where b_name='EmmaT';
+delete from books where num=0;
+```
+
+```mysql 
+#第三题
+create database test03_company charset utf8;
+use test03_company;
+create table department(
+depid int primary key,
+depname varchar(10),
+deinfo varchar(10)
+);
+create table employee(
+empid int primary key,
+`name` varchar(10),
+sex enum('男','女') not null default '男 ',
+title varchar(10),
+birthday datetime,
+depid int,
+foreign key (depid) references department(depid) on update cascade on delete set null
+);
+create table salary(
+empid int primary key,
+dasesalary int ,
+titlesalary int,
+deduction int,
+foreign key (empid) references employee(empid) on update cascade on delete cascade
+);
+insert into department values(111,'生产部',null);
+insert into department values(222,'销售部',null);
+insert into department values(333,'人事部','力职员管理');
+insert into employee values(1001,'张三','男','高级工程师','1975-1-1',111);
+insert into employee values(1002,'李四','女','助工','1985-1-1',111);
+insert into employee values(1003,'王五','男','工程师','1978-11-11',222);
+insert into employee values(1004,'张六','男','工程师','1999-1-1',222);
+insert into salary values(1001,2200,1100,200);
+insert into salary values(1002,1200,200,0);
+insert into salary values(1003,2900,700,200);
+insert into salary values(1004,1950,700,150);
+```
+
+
+
+```mysql
+#第四题
+create database test04_school charset utf8;
+use test04_school;
+create table Department(
+DepNo int(10) primary key not null unique key comment '部门号',
+DepName varchar(20) not null comment '部门名称',
+DepNote varchar(50) comment '部门备注'
+);
+create table Teacher(
+Number int primary key not null unique key comment '教工号',
+`Name` varchar(300) not null comment '姓名',
+Sex enum('男','女') comment '性别',
+Birth date comment '出生日期',
+DepNo int(10) comment '部门号',
+Sakary float comment '工资',
+Address varchar(100) comment '家庭住址' ,
+foreign key (DepNo) references Department(DepNo)
+);
+insert into Department values(601,'软件技术系','软件技术等专业');
+insert into Department values(602,'网络技术系','多媒体技术等专业');
+insert into Department values(603,'艺术设计系','广告艺术设计等专业');
+insert into Department values(604,'管理工程系','连锁经营管理等专业');
+insert into Teacher values(2001,'Tom','女','1970-01-10',602,4500,'四川省锦阳市');
+insert into Teacher values(2002,'Lucy','男','1983-12-18',601,2500,'北京市昌平区');
+insert into Teacher values(2003,'Mike','男','1990-06-01',604,1500,'重庆市渝中区');
+insert into Teacher values(2004,'James','女','1980-10-20',602,3500,'四川省成都市');
+insert into Teacher values(2005,'Jack','男','1975-05-30',603,1200,'重庆市南岸区');
+```
+