Oracle中创建和管理表详解

SQL> /*
SQL> 对于表的操作: 创建表，修改表(添加新的列，改变当前某些列，删除列),删除表
SQL> 创建表: create table(需要create table的权限)
SQL> 修改表: alter table tablename add/modify/drop
SQL> 删除表：drop table tablename
SQL> */
SQL> show user;
USER 为 "SCOTT"
SQL> --访问hr用户下的表
SQL> select * from hr.employees;
select * from hr.employees
                 *
第 1 行出现错误:
ORA-00942: 表或视图不存在
SQL> --测试defaul值
SQL> create table test1
  2  (tid number,
  3   tname varchar(20),
  4   hiredate date default sysdate);
表已创建。
SQL> insert into test1(tid,tname) values(1,'Mary');
已创建 1 行。
SQL> select * from test1;
       TID TNAME                HIREDATE                                                                               
---------- -------------------- --------------                                                                         
         1 Mary                 12-6月 -11                                                                             
SQL> --rowid rownum都是伪列
SQL> select rowid,rownum,empno from emp;
ROWID                  ROWNUM      EMPNO                                                                               
------------------ ---------- ----------                                                                               
AAANA2AAEAAAAAsAAT          1       1122                                                                               
AAANA2AAEAAAAAsAAO          2       1234                                                                               
AAANA2AAEAAAAAsAAP          3       1235                                                                               
AAANA2AAEAAAAAsAAQ          4       2222                                                                               
AAANA2AAEAAAAAsAAR          5       2345                                                                               
AAANA2AAEAAAAAsAAS          6       2346                                                                               
AAANA2AAEAAAAAsAAA          7       7369                                                                               
AAANA