1. 12-1 Copyright  Oracle Corporation, 1998. All rights reserved. What Is a View? EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ----- ------- --------- ----- --------- ----- ----- ------- 7839 KING PRESIDENT 17-NOV-81 5000 10 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30 7782 CLARK MANAGER 7839 09-JUN-81 2450 10 7566 JONES MANAGER 7839 02-APR-81 2975 20 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30 7900 JAMES CLERK 7698 03-DEC-81 950 30 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 7902 FORD ANALYST 7566 03-DEC-81 3000 20 7369 SMITH CLERK 7902 17-DEC-80 800 20 7788 SCOTT ANALYST 7566 09-DEC-82 3000 20 7876 ADAMS CLERK 7788 12-JAN-83 1100 20 7934 MILLER CLERK 7782 23-JAN-82 1300 10 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ----- ------- --------- ----- --------- ----- ----- ------- 7839 KING PRESIDENT 17-NOV-81 5000 10 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30 7782 CLARK MANAGER 7839 09-JUN-81 2450 10 7566 JONES MANAGER 7839 02-APR-81 2975 20 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30 7900 JAMES CLERK 7698 03-DEC-81 950 30 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 7902 FORD ANALYST 7566 03-DEC-81 3000 20 7369 SMITH CLERK 7902 17-DEC-80 800 20 7788 SCOTT ANALYST 7566 09-DEC-82 3000 20 7876 ADAMS CLERK 7788 12-JAN-83 1100 20 7934 MILLER CLERK 7782 23-JAN-82 1300 10 EMP Table EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ----- -------- --------- ---- --------- ------ ----- ------ - 7839 KING PRESIDENT 17-NOV-81 5000 10 7782 CLARK MANAGER 7839 09-JUN-81 1500 300 10 7934 MILLER CLERK 7782 23-JAN-82 1300 10 7566 JONES MANAGER 7839 02-APR-81 2975 20 7788 SCOTT ANALYST 7566 09-DEC-82 3000 20 7876 ADAMS CLERK 7788 12-JAN-83 1100 20 7369 SMITH CLERK 7902 17-DEC-80 800 20 7902 FORD ANALYST 7566 03-DEC-81 3000 20 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30 7900 JAMES CLERK 7698 03-DEC-81 950 30 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ----- -------- --------- ---- --------- ------ ----- ------ - 7839 KING PRESIDENT 17-NOV-81 5000 10 7782 CLARK MANAGER 7839 09-JUN-81 1500 300 10 7934 MILLER CLERK 7782 23-JAN-82 1300 10 7566 JONES MANAGER 7839 02-APR-81 2975 20 7788 SCOTT ANALYST 7566 09-DEC-82 3000 20 7876 ADAMS CLERK 7788 12-JAN-83 1100 20 7369 SMITH CLERK 7902 17-DEC-80 800 20 7902 FORD ANALYST 7566 03-DEC-81 3000 20 7698 BLAKE MANAGER 7839 01-MAY-81 2850 30 7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30 7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30 7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30 7900 JAMES CLERK 7698 03-DEC-81 950 30 7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30 EMPNO ENAME JOB ------ -------- ----------- 7839 KING PRESIDENT 7782 CLARK MANAGER 7934 MILLER CLERK EMPVU10 View EMPVU10 View

2. 12-2 Copyright  Oracle Corporation, 1998. All rights reserved. Simple Views and Complex Views FeatureSimple ViewsComplex Views Number of tablesOneOne or more Contain functionsNoYes Contain groups of dataNoYes DML through viewYesNot always FeatureSimple ViewsComplex Views Number of tablesOneOne or more Contain functionsNoYes Contain groups of dataNoYes DML through viewYesNot always

3. 12-3 Copyright  Oracle Corporation, 1998. All rights reserved. Creating a View You embed a subquery within the CREATE VIEW statement. The subquery can contain complex SELECT syntax. The subquery cannot contain an ORDER BY clause. You embed a subquery within the CREATE VIEW statement. The subquery can contain complex SELECT syntax. The subquery cannot contain an ORDER BY clause. CREATE [OR REPLACE] [FORCE|NOFORCE] VIEW view [(alias[, alias]...)] AS subquery [WITH CHECK OPTION [CONSTRAINT constraint]] [WITH READ ONLY] CREATE [OR REPLACE] [FORCE|NOFORCE] VIEW view [(alias[, alias]...)] AS subquery [WITH CHECK OPTION [CONSTRAINT constraint]] [WITH READ ONLY]

4. 12-4 Copyright  Oracle Corporation, 1998. All rights reserved. Creating a View Create a view, EMPVU10, that contains details of employees in department 10. Describe the structure of the view by using the SQL*Plus DESCRIBE command. SQL> DESCRIBE empvu10 SQL> CREATE VIEW empvu10 2 AS SELECTempno, ename, job 3 FROMemp 4 WHEREdeptno = 10; View created.

5. 12-5 Copyright  Oracle Corporation, 1998. All rights reserved. Querying a View USER_VIEWS USER_VIEWS EMPVU10 SELECTempno, ename, job FROMemp WHEREdeptno = 10; USER_VIEWS USER_VIEWS EMPVU10 SELECTempno, ename, job FROMemp WHEREdeptno = 10; SQL*Plus SELECT * FROM empvu10; EMP 7839KINGPRESIDENT 7782CLARKMANAGER 7934MILLERCLERK

6. 12-6 Copyright  Oracle Corporation, 1998. All rights reserved. Modifying a View Modify the EMPVU10 view by using CREATE OR REPLACE VIEW clause. Add an alias for each column name. Column aliases in the CREATE VIEW clause are listed in the same order as the columns in the subquery. Modify the EMPVU10 view by using CREATE OR REPLACE VIEW clause. Add an alias for each column name. Column aliases in the CREATE VIEW clause are listed in the same order as the columns in the subquery. SQL> CREATE OR REPLACE VIEW empvu10 2 (employee_number, employee_name, job_title) 3 AS SELECT empno, ename, job 4 FROMemp 5 WHEREdeptno = 10; View created.

7. 12-7 Copyright  Oracle Corporation, 1998. All rights reserved. Creating a Complex View Create a complex view that contains group functions to display values from two tables. SQL> CREATE VIEWdept_sum_vu 2 (name, minsal, maxsal, avgsal) 3 AS SELECTd.dname, MIN(e.sal), MAX(e.sal), 4AVG(e.sal) 5 FROMemp e, dept d 6 WHEREe.deptno = d.deptno 7 GROUP BY d.dname; View created.

8. 12-8 Copyright  Oracle Corporation, 1998. All rights reserved. Using the WITH CHECK OPTION Clause You can ensure that DML on the view stays within the domain of the view by using the WITH CHECK OPTION clause. Any attempt to change the department number for any row in the view will fail because it violates the WITH CHECK OPTION constraint. SQL> CREATE OR REPLACE VIEW empvu20 2 AS SELECT* 3 FROM emp 4 WHERE deptno = 20 5 WITH CHECK OPTION CONSTRAINT empvu20_ck; View created.

9. 12-9 Copyright  Oracle Corporation, 1998. All rights reserved. Denying DML Operations You can ensure that no DML operations occur by adding the WITH READ ONLY option to your view definition. SQL> CREATE OR REPLACE VIEW empvu10 2 (employee_number, employee_name, job_title) 3 AS SELECTempno, ename, job 4 FROMemp 5 WHEREdeptno = 10 6 WITH READ ONLY; View created. Any attempt to perform a DML on any row in the view will result in Oracle Server error.

10. 12-10 Copyright  Oracle Corporation, 1998. All rights reserved. Removing a View Remove a view without losing data because a view is based on underlying tables in the database. SQL> DROP VIEW empvu10; View dropped. DROP VIEW view;