/*============创建Customer表==========*/     
create table Customer     
(     
  Customer_id number(6) not null,     
  Customer_name varchar2(50) not null,     
  Password varchar2(20) not null,     
  True_name varchar2(20),     
  Email_address varchar2(50) not null,       --唯一     
  Password_question varchar2(50) not null,     
  Password_anwser varchar2(50) not null,     
  Status char(1),                            --默认是1，取值0或1     
  Customer_level char(1),                    --默认是1，取值1，2，3     
  Score number(6),     
  Register_date date,                        --默认为系统时间     
  Login_time timestamp,     
  Login_count number(6),     
  Login_ip char(6)     
);     
/*===========创建Orders表==========*/     
create table Orders     
(     
   Order_id varchar2(10) not null,     
   Order_Customer_id number(6) not null,     
   Order_date date not null,     
   Order_price number not null    
);     
/*==========查询Customer表===========*/     
select * from Customer     
    
/*==========向表中添加数据===========*/     
insert into Customer values    
(220077,'wantingqiang','wtq','万廷强','lovezhqj@qq.com','你是哪个?','wtq','1','3',150,sysdate,sysdate,15789,'172.26')     
    
/*==========修改表Customer===========*/     
alter table Customer     
    modify Login_ip char(16);     
         
 /*=========修改第一条记录中的ip=====*/     
 update Customer set Login_ip='172.26.3.145' where Customer_id='220077';--ip地址修改成功     
      
 /*=========添加一个列===============*/     
 alter table Customer     
    add LoginOut_time date;                                             --新列增加成功     
         
 /*=========删除一个列LoginOut_time========*/     
 alter table Customer     
    drop column LoginOut_time;                                          --列删除成功     
         
 /*========给列添加注释===========*/     
 comment on column    
     Customer.Customer_Name is '客户姓名';     
      
 /*========给表添加注释==========*/     
 comment on table Customer is '客户表，为了保持与客户的联系';     
      
 /*========重新命名表============*/     
 alter table Customer rename to Customer_Change;     
      
 select * from Customer_Change     
      
 alter table Customer_Change rename to Customer;     
      
 /*==========添加非空约束========*/     
 alter table Customer      
    modify status not null;                                            --非空约束添加成功     
         
 /*==========添加主键约束========*/     
 alter table Customer     
    add constraint customer_id_pk primary key(Customer_id);            --主键添加成功     
      
 /*==========添加外键约束========*/     
 --向Orders表中添加外键，与Customer表关联     
 --在下面的列子末尾加上：     
 --on delete 表示允许级联删除     
 --on update 表示允许级联更新     
 alter table Orders                                                    
    add constraint Orders_Customer_fk  foreign key(Order_Customer_id) references Customer(Customer_id);     
                                                                       --外键添加成功     
 /*==========删除外键约束=========*/     
 alter table Orders     
    drop constraint "ORDERS_CUSTOMER_FK";                              --外键删除成功，这个要注意大小写哈       
      
 /*=========添加唯一约束========*/     
 alter table Customer      
    add constraint un_email unique(Email_address);                     --添加唯一约束成功     
      
      
 /*=========修改默认约束========*/     
 alter table Customer     
    modify Status default('1');     
         
 /*=========添加检查约束========*/     
 alter table Customer     
    add constraint ck_status check(Status in ('1','0'));               --检查约束添加成功     
      
      
 /*==========禁止检查约束=======*/     
 alter table Customer      
    disable constraint ck_status;                                      --禁止成功     
         
 /*==========激活检查约束=======*/     
 alter table Customer     
    enable constraint ck_status;                                       --激活成功     
      
 /*==========删除检查约束========*/     
 alter table Customer     
    drop constraint ck_status;                                         --删除检查约束成功