1. 视图的用途：
1. 限制数据的存取：用户只能看到基表的部分信息
2. 可以使复杂的查询变得容易
3. 提供数据的独立性
2. 简单视图：视图与基表一对一，包含聚合函数的除外，对简单视图修改就是对基表修改
创建视图 V1 SQL> create view v1 as select ename,empno,sal from test where deptno=10; View created. SQL> select * from v1; ENAME EMPNO SAL -------------------- ---------- ---------- CLARK 7782 2450 KING 7839 5000 MILLER 7934 1300 更新视图 SQL> update v1 set ename='aaaa' where empno=7782; 1 row updated. 查看基表变化 SQL> select ename,empno from test where empno=7782; ENAME EMPNO -------------------- ---------- aaaa 7782 SQL> rollback; Rollback complete. SQL> select ename, empno from test where empno=7782; ENAME EMPNO -------------------- ---------- CLARK 7782 SQL>
3. 复杂视图：视图与基表记录一对多，或者包含聚合函数，复杂视图不能被修改，使用聚合函数时，必须要设置别名
1 创建复杂视图 V2 包含聚合函数 2 SQL> create view v2 as select deptno,sum(sal) as SUMSAL from test group by deptno; 3 4 View created. 5 6 SQL> select * from v2; 7 8 DEPTNO SUMSAL 9 ---------- ---------- 10 30 9400 11 20 10875 12 10 8750 13 14 尝试更新复杂视图，出现报错 15 SQL> update v2 set deptno=20 where SUMSAL=9400; 16 update v2 set deptno=20 where SUMSAL=9400 17 * 18 ERROR at line 1: 19 ORA-01732: data manipulation operation not legal on this view 20 21 创建复杂视图 V3 使用多表关联 22 SQL> create view v3 as select t. deptno,sum(sal) as sumsal,d.loc from test t,dept d where t.deptno=d.deptno group by t.deptno,d.loc; 23 24 View created. 25 26 SQL> select * from v3; 27 28 DEPTNO SUMSAL LOC 29 ---------- ---------- -------------------------- 30 20 10875 DALLAS 31 30 9400 CHICAGO 32 10 8750 NEW YORK 33 34 尝试更新复杂视图，出现报错 35 SQL> update v3 set loc='Shanghai' where deptno=20; 36 update v3 set loc='Shanghai' where deptno=20 37 * 38 ERROR at line 1: 39 ORA-01732: data manipulation operation not legal on this view
4. 特殊语句
1. FORCE：在没有基表的前提下，创建视图。用法：SQL> create FORCE VIEW v4 as select * from xxx;
2. WITH CHECK OPTION：对视图WHERE子句进行约束，保证结果集稳定。用法：SQL> create view v5 as select * from emp where deptno=10 WITH CHECK OPTION; ---不能插入非10号部门的数据，不能更改视图中10号部门的数据，但是可以删除数据
3. WITH READ ONLY：禁止对视图进行DML操作。
5. 实验：创建一个简单视图，授权视图给HR用户，查看HR是否有权限查看基表，授权基表给HR，查看HR是否有权限查看视图
1 创建简单视图 V1 2 SQL> create view v1 as select empno,ename from emp where deptno=10; 3 4 View created. 5 6 授权视图SELECT权限给HR 7 SQL> grant select on v1 to hr; 8 9 Grant succeeded. 10 11 SQL> conn hr/hr@erp 12 Connected. 13 14 HR可以查看视图信息 15 SQL> select * from scott.v1; 16 17 EMPNO ENAME 18 ---------- -------------------- 19 7782 CLARK 20 7839 KING 21 7934 MILLER 22 23 HR不能查看基表信息 24 SQL> select * from scott.emp; 25 select * from scott.emp 26 * 27 ERROR at line 1: 28 ORA-00942: table or view does not exist 29 30 SQL> conn scott/tiger@erp 31 Connected. 32 SQL> revoke select on v1 from hr; 33 34 Revoke succeeded. 35 36 授权基表SELECT权限给HR 37 SQL> grant select on emp to hr; 38 39 Grant succeeded. 40 41 SQL> conn hr/hr@erp 42 Connected. 43 44 HR可以查看基表信息 45 SQL> select * from scott.emp where deptno=10; 46 47 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO 48 ---------- -------------------- ------------------ ---------- ------------------- ---------- ---------- ---------- 49 7782 CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10 50 7839 KING PRESIDENT 1981-11-17 00:00:00 5000 10 51 7934 MILLER CLERK 7782 1982-01-23 00:00:00 1300 10 52 53 HR不能查看视图信息 54 SQL> select * from scott.v1; 55 select * from scott.v1 56 * 57 ERROR at line 1: 58 ORA-00942: table or view does not exist