Oracle创建表、约束、视图、索引、序列、同义词、表空间
1、建表
    create table userInfo (
       id number(6),
       name varchar2(20),
       sex number(1),
       age number(3),
       birthday date,
       address varchar2(50),
       email varchar2(25),
       tel number(11)
    );

2、创建约束
    不带约束名称的：
    create table userInfo (
       id number(6) primary key,--主键
       name varchar2(20) not null,--非空
       sex number(1),
       age number(3) default 18,
       birthday date,
       address varchar2(50),
       email varchar2(25) unique,--唯一
       tel number(11),
       deptno number(2) references dept(deptno)—外键
    );
  
    带约束名称：
    create table userInfo (
           id number(6) constraint id_pk primary key,
           name varchar2(20) constraint name_nn not null,
           sex number(1),
           age number(3) default 18,
           birthday date,
           address varchar2(50),
           email varchar2(25) constraint email_uqe unique,
           tel number(11),
           deptno number(2) constraint dept_deptno_ref references dept(deptno)
    );

    列模式：
    create table userInfo (
           id number(6),
           name varchar2(20),
           sex number(1),
           age number(3) default 18,
           birthday date,
           address varchar2(50),
           email varchar2(25),
           tel number(11),
           deptno number(2),
           constraint id_pk primary key (id),--也可以两个以上，联合主键
           constraint dept_deptno_ref foreign key (deptno) references dept(deptno),
           constraint emial_name_uqe unique (email, name)
    );
    Alter模式：
        alter table userInfo add(msn varchar2(20));
        alter table userInfo modify(msn varchar2(25));
        alter table userInfo drop(msn);
       
        alter table userInfo