Oracle中创建和管理表详解

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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                                                                               
AAANA2AAEAAAAAsAAB          8       7499                                                                               
AAANA2AAEAAAAAsAAC          9       7521                                                                               
AAANA2AAEAAAAAsAAD         10       7566                                                                               
AAANA2AAEAAAAAsAAE         11       7654                                                                               
ROWID                  ROWNUM      EMPNO                                                                               
------------------ ---------- ----------                                                                               
AAANA2AAEAAAAAsAAF         12       7698                                                                               
AAANA2AAEAAAAAsAAG         13       7782                                                                               
AAANA2AAEAAAAAsAAH         14       7788                                                                               
AAANA2AAEAAAAAsAAI         15       7839                                                                               
AAANA2AAEAAAAAsAAJ         16       7844                                                                               
AAANA2AAEAAAAAsAAK         17       7876                                                                               
AAANA2AAEAAAAAsAAL         18       7900                                                                               
AAANA2AAEAAAAAsAAM         19       7902                                                                               
AAANA2AAEAAAAAsAAN         20       7934                                                                               
已选择20行。
SQL> --rowid:oracle维护一个地址,该地址指向了该行在硬盘上实际存储的位置
SQL> --关于varchar2和char
SQL> create table testchar
  2  ( c char(5),
  3    v varchar(5));
表已创建。
SQL> insert into testchar values('a','b');
已创建 1 行。
SQL> select * from testchar;
C     V                                                                                                                
----- -----                                                                                                            
a     b                                                                                                                
SQL> select concat(c,'#'),concat(v,'#') from testchar;
CONCAT CONCAT                                                                                                          
------ ------                                                                                                          
a    # b#                                                                                                              
SQL> --添加新列
SQL> alter table testchar
  2  add  hiredate date;
表已更改。
SQL> desc testchar;
 名称                                                              是否为空? 类型
 ----------------------------------------------------------------- -------- --------------------------------------------
 C                                                                          CHAR(5)
 V                                                                          VARCHAR2(5)
 HIREDATE                                                                   DATE
SQL> --修改表
SQL> alter table testchar
  2  modify c char(10);
表已更改。
SQL> desc testchar;
 名称                                                              是否为空? 类型
 ----------------------------------------------------------------- -------- --------------------------------------------
 C                                                                          CHAR(10)
 V                                                                          VARCHAR2(5)
 HIREDATE                                                                   DATE
SQL> --删除列
SQL> alter table testchar
  2  drop hiredate;
drop hiredate
     *
第 2 行出现错误:
ORA-00905: 缺失关键字
SQL> ed
已写入 file afiedt.buf
  1  alter table testchar
  2* drop column hiredate
SQL> /
表已更改。
SQL> desc testchar;
 名称                                                              是否为空? 类型
 ----------------------------------------------------------------- -------- --------------------------------------------
 C                                                                          CHAR(10)
 V                                                                          VARCHAR2(5)
SQL> host cls
SQL> --删除表
SQL> select * from tab;
TNAME                          TABTYPE  CLUSTERID                                                                      
------------------------------ ------- ----------                                                                      
DEPT                           TABLE                                                                                   
EMP                            TABLE                                                                                   
BONUS                          TABLE                                                                                   
SALGRADE                       TABLE                                                                                   
EMP10                          TABLE                                                                                   
EMP101                         TABLE                                                                                   
TEST1                          TABLE                                                                                   
BIN$gNM24ey8RKW0vjhtZ7ZFsA==$0 TABLE                                                                                   
TESTDELETE                     TABLE                                                                                   
TESTCHAR                       TABLE                                                                                   
已选择10行。
SQL> drop table testdelete;
表已删除。
SQL> select * from tab;
TNAME                          TABTYPE  CLUSTERID                                                                      
------------------------------ ------- ----------                                                                      
DEPT                           TABLE                                                                                   
EMP                            TABLE                                                                                   
BONUS                          TABLE                                                                                   
SALGRADE                       TABLE                                                                                   
EMP10                          TABLE                                                                                   
EMP101                         TABLE                                                                                   
TEST1                          TABLE                                                                                   
BIN$gNM24ey8RKW0vjhtZ7ZFsA==$0 TABLE                                                                                   
TESTCHAR                       TABLE                                                                                   
BIN$aJrS9iffT4O1GcD0H3fepg==$0 TABLE                                                                                   
已选择10行。
SQL> --使用purge参数彻底删除表
SQL> drop table test1 purge;
表已删除。
SQL> select * from tab;
TNAME                          TABTYPE  CLUSTERID                                                                      
------------------------------ ------- ----------                                                                      
DEPT                           TABLE                                                                                   
EMP                            TABLE                                                                                   
BONUS                          TABLE                                                                                   
SALGRADE                       TABLE                                                                                   
EMP10                          TABLE                                                                                   
EMP101                         TABLE                                                                                   
BIN$gNM24ey8RKW0vjhtZ7ZFsA==$0 TABLE                                                                                   
TESTCHAR                       TABLE                                                                                   
BIN$aJrS9iffT4O1GcD0H3fepg==$0 TABLE                                                                                   
已选择9行。
SQL> --oracle的回收站
SQL> --查看回收站
SQL> show recyclebin;
ORIGINAL NAME    RECYCLEBIN NAME                OBJECT TYPE  DROP TIME                                                 
---------------- ------------------------------ ------------ -------------------                                       
TESTDELETE       BIN$aJrS9iffT4O1GcD0H3fepg==$0 TABLE        2011-06-12:15:43:34                                       
TESTDELETE       BIN$gNM24ey8RKW0vjhtZ7ZFsA==$0 TABLE        2011-06-12:14:51:43                                       
SQL> --清空回收站
SQL> purge recyclebin;
回收站已清空。
SQL> show recyclebin;
SQL> --关于约束:
SQL> --创建一个表,包含所有约束
SQL> create table myuser
  2  ( userID number constraint pk primary key,
  3    username varchar2(20) constraint c_name not null,
  4    gender   varchar2(2)  constraint c_gender check (gender in ('男','女')),
  5    email    varchar2(20) constraint c_email1 not null
  6                          constraint c_email2 unique
  7    deptno   number constraint fk refereneces dept(deptno)
  8  );
  deptno   number constraint fk refereneces dept(deptno)
  *
第 7 行出现错误:
ORA-00907: 缺失右括号
SQL>   create table myuser
  2  ( userID number constraint pk primary key,
  3    username varchar2(20) constraint c_name not null,
  4    gender   varchar2(2)  constraint c_gender check (gender in ('男','女')),
  5    email    varchar2(20) constraint c_email1 not null
  6                          constraint c_email2 unique,
  7    deptno   number constraint fk refereneces dept(deptno)
  8  );
  deptno   number constraint fk refereneces dept(deptno)
                  *
第 7 行出现错误:
ORA-02253: 此处不允许约束条件说明
SQL> ed
已写入 file afiedt.buf
  1    create table myuser
  2  ( userID number constraint pk primary key,
  3    username varchar2(20) constraint c_name not null,
  4    gender   varchar2(2)  constraint c_gender check (gender in ('男','女')),
  5    email    varchar2(20) constraint c_email1 not null
  6                          constraint c_email2 unique,
  7    deptno   number constraint fk references dept(deptno)
  8* )
SQL> /
表已创建。
SQL> desc myuser;
 名称                                                              是否为空? 类型
 ----------------------------------------------------------------- -------- --------------------------------------------
 USERID                                                            NOT NULL NUMBER
 USERNAME                                                          NOT NULL VARCHAR2(20)
 GENDER                                                                     VARCHAR2(2)
 EMAIL                                                             NOT NULL VARCHAR2(20)
 DEPTNO                                                                     NUMBER
SQL> insert into myuser values(1,'Tom','男','ddd@126.com',10);
已创建 1 行。
SQL> insert into myuser values(1,'Tom','男','ddd@126.com',10);
insert into myuser values(1,'Tom','男','ddd@126.com',10)
*
第 1 行出现错误:
ORA-00001: 违反唯一约束条件 (SCOTT.PK)
SQL> insert into myuser values(2,'Tom','啊','ddd@126.coddm',10);
insert into myuser values(2,'Tom','啊','ddd@126.coddm',10)
*
第 1 行出现错误:
ORA-02290: 违反检查约束条件 (SCOTT.C_GENDER)
SQL> --触发器也可以检查数据的正确与否
SQL> spool off

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