alter table userInfo add(msn varchar2(20));

?

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 (<