oracle alter table 详解

//建测试表 
create table dept( 
       deptno number(3) primary key, 
       dname varchar2(10), 
       loc varchar2(13)  
       ); 
create table employee_info( 
       empno number(3), 
       deptno number(3), 
       ename varchar2(10), 
       sex char(1), 
       phone number(11), 
       address varchar2(50), 
       introduce varchar2(100) 
       ); 
-- 
//0.重命名 
  //0.1 表:rename dept to dt; 
           rename dt to dept; 
  //0.2 列:alter table dept rename column loc to location; 
           alter table dept rename column location to loc; 
//1.添加约束 
  //1.1 primary key 
      alter table employee_info add constraint pk_emp_info primary key(empno); 
  //1.2 foreign key 
      alter table employee_info add constraint fk_emp_info foreign key(deptno) 
      references dept(deptno); 
  //1.3 check 
      alter table employee_info add constraint ck_emp_info check 
      (sex in ('F','M')); 
  //1.4 not null 
      alter table employee_info modify phone constraint not_null_emp_info not null; 
  //1.5 unique 
      alter table employee_info add constraint uq_emp_info unique(phone); 
  //1.6 default 
      alter table employee_info modify sex char(2) default 'M'; 
//2.添加列 
   alter table employee_info add id varchar2(18); 
   alter table employee_info add hiredate date default sysdate not null; 
//3.删除列 
   alter table employee_info drop column introduce; 
//3.修改列 
  //3.1 修改列的长度 
      alter table dept modify loc varchar2(50); 
  //3.2 修改列的精度 
      alter table employee_info modify empno number(2); 
  //3.3 修改列的数据类型 
      alter table employee_info modify sex char(2); 
  //3.4 修改默认值 
      alter table employee_info modify hiredate default sysdate+1; 
//4.禁用约束 
  alter table employee_info disable constraint uq_emp_info; 
//5.启用约束 
  alter table employee_info enable constraint uq_emp_info; 
//6.延迟约束 
  alter table employee_info drop constraint fk_emp_info; 
  alter table employee_info add constraint fk_emp_info foreign key(deptno) 
        references dept(deptno) 
  deferrable initially deferred; 
//7.向表中添加注释 
  comment on table employee_info is 'information of employees'; 
//8.向列添加注释 
  comment on column employee_info.ename is 'the name of employees'; 
  comment on column dept.dname is 'the name of department'; 
//9.清除表中所有数据 
  truncate table employee_info; 
//10.删除表 
  drop table employee_info;