Modifyingi i a Viewi

•• Modifyify thet EMPVU10 viewi by usingi

CREATE OR REPLACE VIEWI clausel .. Add an aliasli forf r each columnl name..


SQL>	CREATE OR REPLACE VIEW empvu10
2		(employee_number, employee_name,	jo
3	AS SELECT	empno, ename, job
4	FROM	emp
5	WHERE	deptno =	10;
View	created.

•• Columnl aliasesli inin thet CREATE VIEWI clausel arere listedli t inin thet same orderr r as thet columnsl inin thet subqueryry..

12-12

Creatingi a Complexl Viewi

Create a complex view that contains group functions to display values from two tables.


SQL>	CREATE VIEW	dept_sum_vu
2		(name,	minsa
3	AS SELECT	d.dname, MIN(e.sal), MAX(e.sal),
4		AVG(e.sal)
5	FROM	emp e, dept
6	WHERE	e.deptno = d
7	GROUP BY	d.dname;
View	created.

12-13

Rulesl for Performingi DML Operationsi on a Viewi

•• You can performrf rm DML operationsr ti on simplei le viewsi ..

•• You cannott remover a rowr ifif thet viewi containst i thet following:f ll i :

–Groupr functionsf ti

–A GROUP BY clausel

–The DISTINCTI I keywordrd

12-14

Rulesl for Performingi DML Operationsi on a Viewi

•• You cannott modifyify datata inin a viewi ifif itit contains:t i :

–Any off thet conditionsiti mentionedti inin thet previousr i slideli

–Columnsl definedfi by expressionsr i

–The ROWNUM pseudocolumnl

•• You cannott add datata if:if:

–The viewi containst i any off thet conditionsiti mentionedti above orr inin thet previousr i slideli

–Therere arere NOT NULL columnsl inin thet base tablest l thatt t arere nott selectedl t by thet viewi

12-15

Usingi the WITHI CHECK OPTIONI

Clausel

•• You can ensurere thatt t DML on thet viewi stayst withinit in thet domainin off thet viewi by usingi thet WITHI CHECK OPTIONI ..


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.

•• Any attempttt t toto change thet departmentrt t numberr forf r any rowr inin thet viewi willill failf il because itit violatesi l t thet WITHI CHECK OPTIONI constrainttr i t..

12-16

Denyingi DML Operationsi

•• You can ensurere thatt t no DML operationsr ti occurr by addingi thet WITHI READ ONLY optionti toto yourr viewi definitionfi iti ..


SQL>	CREATE OR REPLACE VIEW empvu10
2	(employee_number, employee_name, job_title)
3	AS SELECT	empno, ename, job
4	FROM	emp
5	WHERE	deptno	=	10
6	WITH READ ONLY;
View	created.