ORACLE数据库对象——同义词、序列、视图

ORACLE数据库对象
——同义词、序列、视图
同义词：同义词是现有对象的别名
简化SQL语句
隐藏对象的名称和所有者
提供对对象的公共访问

同义词分为私有同义词和公有同义词
私有同义词只能在其模式内访问，且不能与当前模式的对象同名。
公有同义词可被所有的数据库用户访问。

以 SYS 用户登录
SQL> CONNECT SYS/SYS AS SYSDBA;
Connected to Oracle9i Enterprise Edition Release 9.2.0.1.0
Connected as SYS

创建私有同义词
SQL> CREATE SYNONYM synemp FOR SCOTT.emp;

Synonym created

SQL> select * from synemp;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
----- ---------- --------- ----- ----------- --------- --------- ------
7369 SMITH CLERK 7902 1980-12-17 800.00 20
7499 ALLEN SALESMAN 7698 1981-2-20 1600.00 300.00 30
7521 WARD SALESMAN 7698 1981-2-22 1250.00 500.00 30
7566 JONES MANAGER 7839 1981-4-2 2975.00 20
7654 MARTIN SALESMAN 7698 1981-9-28 1250.00 1400.00 30
7698 BLAKE MANAGER 7839 1981-5-1 2850.00 30
7782 CLARK MANAGER 7839 1981-6-9 2450.00 10
7788 SCOTT ANALYST 7566 1987-4-19 3000.00 20
7839 KING PRESIDENT 1981-11-17 5000.00 10
7844 TURNER SALESMAN 7698 1981-9-8 1500.00 0.00 30
7876 ADAMS CLERK 7788 1987-5-23 1100.00 20
7900 JAMES CLERK 7698 1981-12-3 950.00 30
7902 FORD ANALYST 7566 1981-12-3 3000.00 20
7934 MILLER CLERK 7782 1982-1-23 1300.00 10

14 rows selected

查询创建的同义词

SQL> select * from user_synonyms; SYNONYM_NAME TABLE_OWNER TABLE_NAME DB_LINK ------------------------------ ------------------------------ ------------------------------ -------------------------------------------------------------------------------- DEF$_AQCALL SYSTEM DEF$_AQCALL DEF$_CALLDEST SYSTEM DEF$_CALLDEST DEF$_DEFAULTDEST SYSTEM DEF$_DEFAULTDEST DEF$_ERROR SYSTEM DEF$_ERROR DEF$_LOB SYSTEM DEF$_LOB DEF$_SCHEDULE SYSTEM DEF$_SCHEDULE EMP SCOTT EMP 7 rows selected

SQL> select OBJECT_NAME,OBJECT_TYPE from user_objects where object_type='SYNONYM'; OBJECT_NAME OBJECT_TYPE ---------------------------------------------------------------- ------------ DEF$_AQCALL SYNONYM DEF$_CALLDEST SYNONYM DEF$_DEFAULTDEST SYNONYM DEF$_ERROR SYNONYM DEF$_LOB SYNONYM DEF$_SCHEDULE SYNONYM EMP SYNONYM 7 rows selected

SQL> select * from dict where instr(comments,'SYNONYM')>0; TABLE_NAME COMMENTS ----------------- ---------------------------------------------------------------------- SYN Synonym for USER_SYNONYMS SQL> select * from SYN; SYNONYM_NAME TABLE_OWNER TABLE_NAME DB_LINK ------------------------------ ------------------------------ ------------------------------ -------------------------------------------------------------------------------- DEF$_AQCALL SYSTEM DEF$_AQCALL DEF$_CALLDEST SYSTEM DEF$_CALLDEST DEF$_DEFAULTDEST SYSTEM DEF$_DEFAULTDEST DEF$_ERROR SYSTEM DEF$_ERROR DEF$_LOB SYSTEM DEF$_LOB DEF$_SCHEDULE SYSTEM DEF$_SCHEDULE EMP SCOTT EMP 7 rows selected

SQL> select * from dict where instr(comments,'synonym')>0; TABLE_NAME COMMENTS ----------------- ---------------------------------------------------------------------- ALL_CATALOG All tables, views, synonyms, sequences accessible to the user ALL_POLICY_CONTEXTS All policy driving context defined for all synonyms, tables, or views accessable ALL_POLICY_GROUPS All policy groups defined for any synonym, table or view accessable to the user ALL_SYNONYMS All synonyms accessible to the user DBA_AUDIT_OBJECT Audit trail records for statements concerning objects, specifically: table, clus DBA_POLICY_CONTEXTS All policy driving context defined for any synonym, table, or view in the databa DBA_POLICY_GROUPS All policy groups defined for any synonym, table, view in the database DBA_SYNONYMS All synonyms in the database USER_AUDIT_OBJECT Audit trail records for statements concerning objects, specifically: table, clus USER_POLICIES All row level security policies for synonyms, tables, or views owned by the user USER_POLICY_CONTEXTS All policy driving context defined for synonyms, tables, or views in current sch USER_POLICY_GROUPS All policy groups defined for any synonym, table, or view USER_SYNONYMS The user's private synonyms 13 rows selected SQL> select * from USER_SYNONYMS; SYNONYM_NAME TABLE_OWNER TABLE_NAME DB_LINK ------------------------------ ------------------------------ ------------------------------ -------------------------------------------------------------------------------- DEF$_AQCALL SYSTEM DEF$_AQCALL DEF$_CALLDEST SYSTEM DEF$_CALLDEST DEF$_DEFAULTDEST SYSTEM DEF$_DEFAULTDEST DEF$_ERROR SYSTEM DEF$_ERROR DEF$_LOB SYSTEM DEF$_LOB DEF$_SCHEDULE SYSTEM DEF$_SCHEDULE EMP SCOTT EMP 7 rows selected

创建公有同义词
SQL> CREATE PUBLIC SYNONYM emp_syn FOR SCOTT.emp;

Synonym created

查询公有同义词

SQL> select * from ALL_SYNONYMS where SYNONYM_NAME='emp_syn';

OWNER SYNONYM_NAME TABLE_OWNER TABLE_NAME DB_LINK
---------- ------------------- ------------------- ------------------- --------

SQL> select * from ALL_SYNONYMS where SYNONYM_NAME='EMP_SYN';

OWNER SYNONYM_NAME TABLE_OWNER TABLE_NAME DB_LINK
---------- ------------------ ------------------- ------------------- --------
PUBLIC EMP_SYN SCOTT EMP

SQL> select * from all_objects where OBJECT_NAME='emp_syn';

OWNER OBJECT_NAME SUBOBJECT_NAME OBJECT_ID DATA_OBJECT_ID OBJECT_TYPE
------ ----------- -------------- --------- -------------- -----------

CREATED LAST_DDL_TIME TIMESTAMP STATUS TEMPORARY GENERATED
----------- ------------- ------------------ ------ --------- ---------

SQL> select * from all_objects where OBJECT_NAME='EMP_SYN';

OWNER OBJECT_NAME SUBOBJECT_NAME OBJECT_ID DATA_OBJECT_ID OBJECT_TYPE
------ ----------- -------------- --------- -------------- -----------
PUBLIC EMP_SYN 30308 SYNONYM

CREATED LAST_DDL_TIME TIMESTAMP STATUS TEMPORARY GENERATED
----------- ------------- ------------------ ------ --------- ---------
2008-8-19 0 2008-8-19 0:0 2008-8-19:00:09:07 VALID N N

创建或替换现有的同义词
CREATE OR REPLACE SYNONYM emp_syn FOR SCOTT.emp;
删除同义词
DROP SYNONYM emp;
DROP PUBLIC SYNONYM emp_syn;

序列：用于生成唯一、连续序号的对象；序列可以是升序的，也可以是降序的
CREATE SEQUENCE emp_seq
START WITH 10 指定第一个序号从10开始
INCREMENT BY 10 指定序号之间的间隔为10
MAXVALUE 2000 表示序列的最大值为2000
MINVALUE 10 表示序列的最小值为10
NOCYCLE 达到最大值后停止生成下一个值
CACHE 10; 指定内存中预先分配的序号数
START WITH 默认值1
INCREMENT BY 默认值1
CACHE 默认值20
如果指定循环CYCLE，必须指定MINVALUE 与START WITH一致 且必须指定MAXVALUE；一般情况MAXVALUE 、MINVALUE、CYCLE同时使用才具有意义，否则无意义。

CREATE SEQUENCE emp_seq START WITH 8000 INCREMENT BY 100 MAXVALUE 8200 MINVALUE 8000 CYCLE CACHE 10 ORA-04013: CACHE 值必须小于 CYCLE 值

CACHE值必须小于CYCLE 值

CREATE SEQUENCE emp_seq START WITH 8000 INCREMENT BY 100 MAXVALUE 8200 MINVALUE 8000 CYCLE CACHE 10 Sequence created

通过序列的伪列来访问序列的值

SQL> SELECT emp_seq.CURRVAL FROM dual; SELECT emp_seq.CURRVAL FROM dual ORA-08002: 序列EMP_SEQ.CURRVAL 尚未在此进程中定义

CURRVAL必须在执行过最少一次NEXTVAL后调用

SQL> SELECT emp_seq.NEXTVAL FROM dual; 第一次执行NEXTVAL NEXTVAL ---------- 8000 SQL> SELECT emp_seq.CURRVAL FROM dual; CURRVAL ---------- 8000

SQL> INSERT INTO EMP(EMPNO,ENAME) VALUES(emp_seq.NEXTVAL,'HUANGPei'); 1 row inserted

SQL> SELECT emp_seq.CURRVAL FROM dual; CURRVAL ---------- 8100 SQL> SELECT emp_seq.NEXTVAL FROM dual; NEXTVAL ---------- 8200

SQL> SELECT * FROM EMP; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ----- ---------- --------- ----- ----------- --------- --------- ------ 7369 SMITH CLERK 7902 1980-12-17 800.00 20 7499 ALLEN SALESMAN 7698 1981-2-20 1600.00 300.00 30 7521 WARD SALESMAN 7698 1981-2-22 1250.00 500.00 30 7566 JONES MANAGER 7839 1981-4-2 2975.00 20 7654 MARTIN SALESMAN 7698 1981-9-28 1250.00 1400.00 30 7698 BLAKE MANAGER 7839 1981-5-1 2850.00 30 7782 CLARK MANAGER 7839 1981-6-9 2450.00 10 7788 SCOTT ANALYST 7566 1987-4-19 3000.00 20 7839 KING PRESIDENT 1981-11-17 5000.00 10 7844 TURNER SALESMAN 7698 1981-9-8 1500.00 0.00 30 7876 ADAMS CLERK 7788 1987-5-23 1100.00 20 7900 JAMES CLERK 7698 1981-12-3 950.00 30 7902 FORD ANALYST 7566 1981-12-3 3000.00 20 7934 MILLER CLERK 7782 1982-1-23 1300.00 10 8100 HUANGPei 15 rows selected

使用ALTER SEQUENCE语句修改序列， 不能更改序列的START WITH参数 ALTER SEQUENCE emp_seq MAXVALUE 5000 CYCLE; 使用DROP SEQUENCE语句删除序列 DROP SEQUENCE emp_seq;

视图：以经过定制的方式显示来自一个或多个表的数据
视图可以视为“虚拟表”或“存储的查询”
创建视图所依据的表称为“基表”
视图的优点有：
提供了另外一种级别的表安全性
隐藏的数据的复杂性
简化的用户的SQL命令
隔离基表结构的改变
通过重命名列，从另一个角度提供数据

SQL> CREATE VIEW emp_view 2 AS 3 SELECT * FROM EMP; View created SQL> SELECT * FROM emp_view; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ----- ---------- --------- ----- ----------- --------- --------- ------ 7369 SMITH CLERK 7902 1980-12-17 800.00 20 7499 ALLEN SALESMAN 7698 1981-2-20 1600.00 300.00 30 7521 WARD SALESMAN 7698 1981-2-22 1250.00 500.00 30 7566 JONES MANAGER 7839 1981-4-2 2975.00 20 7654 MARTIN SALESMAN 7698 1981-9-28 1250.00 1400.00 30 7698 BLAKE MANAGER 7839 1981-5-1 2850.00 30 7782 CLARK MANAGER 7839 1981-6-9 2450.00 10 7788 SCOTT ANALYST 7566 1987-4-19 3000.00 20 7839 KING PRESIDENT 1981-11-17 5000.00 10 7844 TURNER SALESMAN 7698 1981-9-8 1500.00 0.00 30 7876 ADAMS CLERK 7788 1987-5-23 1100.00 20 7900 JAMES CLERK 7698 1981-12-3 950.00 30 7902 FORD ANALYST 7566 1981-12-3 3000.00 20 7934 MILLER CLERK 7782 1982-1-23 1300.00 10 8100 HUANGPei 15 rows selected

SQL> CREATE OR REPLACE VIEW emp_view 2 AS 3 SELECT EMPNO,ENAME,SAL FROM EMP; View created SQL> SELECT * FROM emp_view; EMPNO ENAME SAL ----- ---------- --------- 7369 SMITH 800.00 7499 ALLEN 1600.00 7521 WARD 1250.00 7566 JONES 2975.00 7654 MARTIN 1250.00 7698 BLAKE 2850.00 7782 CLARK 2450.00 7788 SCOTT 3000.00 7839 KING 5000.00 7844 TURNER 1500.00 7876 ADAMS 1100.00 7900 JAMES 950.00 7902 FORD 3000.00 7934 MILLER 1300.00 8100 HUANGPei 15 rows selected

SQL> CREATE VIEW error_view 2 AS 3 SELECT * FROM HP; CREATE VIEW error_view AS SELECT * FROM HP ORA-00942: 表或视图不存在

SQL> CREATE FORCE VIEW error_view 2 AS 3 SELECT * FROM HP; Warning: View created with compilation errors SQL> CREATE TABLE HP 2 AS 3 SELECT EMPNO,ENAME FROM EMP; Table created SQL> SELECT * FROM error_view; EMPNO ENAME ----- ---------- 7369 SMITH 7499 ALLEN 7521 WARD 7566 JONES 7654 MARTIN 7698 BLAKE 7782 CLARK 7788 SCOTT 7839 KING 7844 TURNER 7876 ADAMS 7900 JAMES 7902 FORD 7934 MILLER 8100 HUANGPei 15 rows selected

SQL> CREATE VIEW emp_sal_view 2 AS 3 SELECT EMPNO,ENAME,SAL FROM EMP WHERE SAL>=3000; View created SQL> SELECT * FROM emp_sal_view; EMPNO ENAME SAL ----- ---------- --------- 7788 SCOTT 3000.00 7839 KING 5000.00 7902 FORD 3000.00 SQL> UPDATE emp_sal_view SET SAL=2000 WHERE EMPNO=7788; 1 row updated SQL> SELECT * FROM emp_sal_view; EMPNO ENAME SAL ----- ---------- --------- 7839 KING 5000.00 7902 FORD 3000.00

SQL> CREATE OR REPLACE VIEW emp_sal_view 2 AS 3 SELECT EMPNO,ENAME,SAL FROM EMP WHERE SAL>=3000 4 WITH CHECK OPTION; View created SQL> SELECT * FROM emp_sal_view; EMPNO ENAME SAL ----- ---------- --------- 7788 SCOTT 3000.00 7839 KING 5000.00 7902 FORD 3000.00 SQL> UPDATE emp_sal_view SET SAL=2000 WHERE EMPNO=7788; UPDATE emp_sal_view SET SAL=2000 WHERE EMPNO=7788 ORA-01402: 视图 WITH CHECK OPTIDN 违反 where 子句

SQL> CREATE OR REPLACE VIEW emp_sal_view 2 AS 3 SELECT * FROM EMP; View created SQL> SELECT * FROM emp_sal_view; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ----- ---------- --------- ----- ----------- --------- --------- ------ 7369 SMITH CLERK 7902 1980-12-17 800.00 20 7499 ALLEN SALESMAN 7698 1981-2-20 1600.00 300.00 30 7521 WARD SALESMAN 7698 1981-2-22 1250.00 500.00 30 7566 JONES MANAGER 7839 1981-4-2 2975.00 20 7654 MARTIN SALESMAN 7698 1981-9-28 1250.00 1400.00 30 7698 BLAKE MANAGER 7839 1981-5-1 2850.00 30 7782 CLARK MANAGER 7839 1981-6-9 2450.00 10 7788 SCOTT ANALYST 7566 1987-4-19 3000.00 20 7839 KING PRESIDENT 1981-11-17 5000.00 10 7844 TURNER SALESMAN 7698 1981-9-8 1500.00 0.00 30 7876 ADAMS CLERK 7788 1987-5-23 1100.00 20 7900 JAMES CLERK 7698 1981-12-3 950.00 30 7902 FORD ANALYST 7566 1981-12-3 3000.00 20 7934 MILLER CLERK 7782 1982-1-23 1300.00 10 8100 HUANGPei 15 rows selected SQL> UPDATE emp_sal_view SET SAL=20000 WHERE EMPNO=8100; 1 row updated SQL> SELECT * FROM emp_sal_view; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ----- ---------- --------- ----- ----------- --------- --------- ------ 7369 SMITH CLERK 7902 1980-12-17 800.00 20 7499 ALLEN SALESMAN 7698 1981-2-20 1600.00 300.00 30 7521 WARD SALESMAN 7698 1981-2-22 1250.00 500.00 30 7566 JONES MANAGER 7839 1981-4-2 2975.00 20 7654 MARTIN SALESMAN 7698 1981-9-28 1250.00 1400.00 30 7698 BLAKE MANAGER 7839 1981-5-1 2850.00 30 7782 CLARK MANAGER 7839 1981-6-9 2450.00 10 7788 SCOTT ANALYST 7566 1987-4-19 3000.00 20 7839 KING PRESIDENT 1981-11-17 5000.00 10 7844 TURNER SALESMAN 7698 1981-9-8 1500.00 0.00 30 7876 ADAMS CLERK 7788 1987-5-23 1100.00 20 7900 JAMES CLERK 7698 1981-12-3 950.00 30 7902 FORD ANALYST 7566 1981-12-3 3000.00 20 7934 MILLER CLERK 7782 1982-1-23 1300.00 10 8100 HUANGPei 20000.00 15 rows selected

SQL> CREATE OR REPLACE VIEW emp_sal_view 2 AS 3 SELECT * FROM EMP 4 WITH READ ONLY; View created SQL> SELECT * FROM emp_sal_view; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ----- ---------- --------- ----- ----------- --------- --------- ------ 7369 SMITH CLERK 7902 1980-12-17 800.00 20 7499 ALLEN SALESMAN 7698 1981-2-20 1600.00 300.00 30 7521 WARD SALESMAN 7698 1981-2-22 1250.00 500.00 30 7566 JONES MANAGER 7839 1981-4-2 2975.00 20 7654 MARTIN SALESMAN 7698 1981-9-28 1250.00 1400.00 30 7698 BLAKE MANAGER 7839 1981-5-1 2850.00 30 7782 CLARK MANAGER 7839 1981-6-9 2450.00 10 7788 SCOTT ANALYST 7566 1987-4-19 3000.00 20 7839 KING PRESIDENT 1981-11-17 5000.00 10 7844 TURNER SALESMAN 7698 1981-9-8 1500.00 0.00 30 7876 ADAMS CLERK 7788 1987-5-23 1100.00 20 7900 JAMES CLERK 7698 1981-12-3 950.00 30 7902 FORD ANALYST 7566 1981-12-3 3000.00 20 7934 MILLER CLERK 7782 1982-1-23 1300.00 10 8100 HUANGPei 20000.00 15 rows selected SQL> UPDATE emp_sal_view SET DEPTNO=10 WHERE EMPNO=8100; UPDATE emp_sal_view SET DEPTNO=10 WHERE EMPNO=8100 ORA-01733: 此处不允许虚拟列

SQL> CREATE OR REPLACE VIEW emp_dept_view 2 AS 3 SELECT E.EMPNO,E.ENAME,E.SAL,D.DEPTNO,D.DNAME FROM EMP E,DEPT D 4 WHERE E.DEPTNO=D.DEPTNO; View created SQL> SELECT * FROM emp_dept_view; EMPNO ENAME SAL DEPTNO DNAME ----- ---------- --------- ------ -------------- 7369 SMITH 800.00 20 RESEARCH 7499 ALLEN 1600.00 30 SALES 7521 WARD 1250.00 30 SALES 7566 JONES 2975.00 20 RESEARCH 7654 MARTIN 1250.00 30 SALES 7698 BLAKE 2850.00 30 SALES 7782 CLARK 2450.00 10 ACCOUNTING 7788 SCOTT 3000.00 20 RESEARCH 7839 KING 5000.00 10 ACCOUNTING 7844 TURNER 1500.00 30 SALES 7876 ADAMS 1100.00 20 RESEARCH 7900 JAMES 950.00 30 SALES 7902 FORD 3000.00 20 RESEARCH 7934 MILLER 1300.00 10 ACCOUNTING 14 rows selected SQL> UPDATE emp_dept_view SET ENAME='HUANGPei' WHERE EMPNO=7369; 1 row updated SQL> UPDATE emp_dept_view SET DNAME='ACCOUNTING' WHERE EMPNO=7369; UPDATE emp_dept_view SET DNAME='ACCOUNTING' WHERE EMPNO=7369 ORA-01779: 无法修改与非键值保存表对应的列 SQL> SELECT * FROM emp_dept_view; EMPNO ENAME SAL DEPTNO DNAME ----- ---------- --------- ------ -------------- 7369 HUANGPei 800.00 20 RESEARCH 7499 ALLEN 1600.00 30 SALES 7521 WARD 1250.00 30 SALES 7566 JONES 2975.00 20 RESEARCH 7654 MARTIN 1250.00 30 SALES 7698 BLAKE 2850.00 30 SALES 7782 CLARK 2450.00 10 ACCOUNTING 7788 SCOTT 3000.00 20 RESEARCH 7839 KING 5000.00 10 ACCOUNTING 7844 TURNER 1500.00 30 SALES 7876 ADAMS 1100.00 20 RESEARCH 7900 JAMES 950.00 30 SALES 7902 FORD 3000.00 20 RESEARCH 7934 MILLER 1300.00 10 ACCOUNTING 14 rows selected

在视图上也可以使用修改数据的DML语句，如INSERT、UPDATE和DELETE 视图上的DML语句有如下限制： 只能修改一个底层的基表 如果修改违反了基表的约束条件，则无法更新视图 如果视图包含连接操作符、DISTINCT 关键字、集合操作符、聚合函数或 GROUP BY 子句，则将无法更新视图 如果视图包含伪列或表达式，则将无法更新视图