视图定义：视图是一个已经被命名的查询语句
创建视图必须有创建视图的权限
--** select * from session_privs;
PRIVILEGE ---------------------------------------- CREATE SESSION UNLIMITED TABLESPACE CREATE TABLE CREATE CLUSTER CREATE VIEW CREATE SEQUENCE SELECT ANY SEQUENCE CREATE DATABASE LINK CREATE PROCEDURE CREATE TRIGGER CREATE MATERIALIZED VIEW CREATE TYPE CREATE OPERATOR CREATE INDEXTYPE 14 rows selected. Elapsed: 00:00:00.00
创建视图
create view v_emp as select * from emp where deptno=20;
select * from v_emp;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
7369 SMITH CLERK 7902 17-DEC-80 800 20
7566 JONES MANAGER 7839 02-APR-81 2975 20
7788 SCOTT ANALYST 7566 19-APR-87 3000 20
7876 ADAMS CLERK 7788 23-MAY-87 1100 20
7902 FORD ANALYST 7566 03-DEC-81 3000 20
Elapsed: 00:00:00.01
修改视图
create or replace view v_emp as select * from emp where deptno=10;
删除视图
drop view v_emp;
创建复杂视图
create or replace view v_emp as select e.ename,d.dname from emp e,dept d where e.deptno=d.deptno;
select * from v_emp;
ENAME DNAME ---------- -------------- SMITH RESEARCH ALLEN SALES WARD SALES JONES RESEARCH MARTIN SALES BLAKE SALES CLARK ACCOUNTING SCOTT RESEARCH KING ACCOUNTING TURNER SALES ADAMS RESEARCH JAMES SALES FORD RESEARCH MILLER ACCOUNTING 14 rows selected. Elapsed: 00:00:00.02
如果要对视图进行insert操作，要求视图中不能有组函数、group by、distinct、rownum
如果要对视图进行update操作，要求视图中不能有组函数、group by、distinct、rownum、计算生成的伪列
如果要对视图进行insert操作，要求视图中不能有组函数、group by、distinct、rownum、计算生成的表达式，而且必须有非空约束的列。
重新准备实验需要的基表
create or replace view v_emp as select ename,sal,dname from e1 where dname='SALES';
select * from e1;
ENAME SAL COMM DNAME ---------- ---------- ---------- -------------- SMITH 800 RESEARCH ALLEN 1600 300 SALES WARD 1250 500 SALES JONES 2975 RESEARCH MARTIN 1250 1400 SALES BLAKE 2850 SALES CLARK 2450 ACCOUNTING SCOTT 3000 RESEARCH KING 5000 ACCOUNTING TURNER 1500 0 SALES ADAMS 1100 RESEARCH JAMES 950 SALES FORD 3000 RESEARCH MILLER 1300 ACCOUNTING 15 rows selected. Elapsed: 00:00:00.01
select * from v_EMP;
ENAME SAL DNAME ---------- ---------- -------------- ALLEN 1600 SALES WARD 1250 SALES MARTIN 1250 SALES BLAKE 2850 SALES TURNER 1500 SALES JAMES 950 SALES 6 rows selected. Elapsed: 00:00:00.00
insert into v_emp values('tt',1230,'SALES');
select * from v_emp;
ENAME SAL DNAME ---------- ---------- -------------- ALLEN 1600 SALES WARD 1250 SALES MARTIN 1250 SALES BLAKE 2850 SALES TURNER 1500 SALES JAMES 950 SALES tt 1230 SALES 7 rows selected. Elapsed: 00:00:00.00
创建带约束的视图
create or replace view v_emp as select ename,sal,dname from e1 where dname='SALES' with check option;
select * from v_emp;
ENAME SAL DNAME ---------- ---------- -------------- ALLEN 1600 SALES WARD 1250 SALES MARTIN 1250 SALES BLAKE 2850 SALES TURNER 1500 SALES JAMES 950 SALES tt 1230 SALES 7 rows selected. Elapsed: 00:00:00.01
insert into v_emp values('aa',112,'sales');
insert into v_emp values('aa',112,'sales')
*
ERROR at line 1:
ORA-01402: view WITH CHECK OPTION where-clause violation
Elapsed: 00:00:00.00
insert into v_emp values('aa',112,'SALES');
select * from v_emp;
ENAME SAL DNAME ---------- ---------- -------------- ALLEN 1600 SALES WARD 1250 SALES MARTIN 1250 SALES BLAKE 2850 SALES TURNER 1500 SALES JAMES 950 SALES tt 1230 SALES aa 112 SALES 8 rows selected.
只读视图
create or replace view v_emp as select ename,sal,dname from e1 where dname='SALES' with read only;
insert into v_emp values('aa',112,'SALES');
insert into v_emp values('aa',112,'SALES')
*
ERROR at line 1:
ORA-42399: cannot perform a DML operation on a read-only view
Elapsed: 00:00:00.00
如果创建了视图，就可以从数据字典中查询到创建视图的语句
--** select text from user_views where view_name='V_EMP';
TEXT -------------------------------------------------------------------------------- select ename,sal,dname from e1 where dname='SALES' with read only Elapsed: 00:00:00.02