Create a outlook in Oracle

Oracle database objects are divided into 5 kinds: tables, views, sequences, indexes and synonyms.
view is based on 1 or extra tables or views of the plausible form itself does not contain data, through which the data inside the table can be queried and modified. View based on table for base table.
view is stored in the data lexicon of a select statement. Data can be extracted by creating a logical view on the collection or portfolio.
view of the advantages:
1. access to the database,Nike Shox NZ, because you can selectively view the culling as chapter of the database.
2. user through a simple query to get results from a complex query.
3. to maintain the independence of the file,Women's Air Max 2009, attempting to retake file from multiple charts.
4. for the same data can produce assorted view.
view is divided into a uncomplicated view and complicated view:
simply view only access to data from a unattached table
; complex view from multiple tables

simple view does not contain functions and data sets
complex view namely contains
simple view of DML operation can not
complex view.
view creation:
; CREATE [OR REPLACE] [FORCE | NOFORCE] VIEW view_name
[(alias [, alias ]...)]
AS subquery
[WITH CHECK OPTION [CONSTRAINT constraint
[WITH READ ONLY]

OR REPLACE: if trying to create yet exists, ORACLE automatically rebuild the view;
FORCE : Regardless of the subsistence of the base table will automatically create the ORACLE view;
NOFORCE: only ORACLE bottom tables exist only to create the view:
alias : To view the definition of aliases generated columns;
subquery: a complete SELECT statement, the statement can be defined in an alias;
WITH CHECK OPTION:
insert or modify rows of data view definition must satisfy the constraints;
WITH READ ONLY:
; can not view anyone of the DML operation.
For example:
CREATE OR REPLACE VIEW dept_sum_vw
(name, minsal, maxsal, avgsal)
AS SELECT d.dname, min (e.sal), max (e.sal),Men's Air Max 90, avg (e.sal)
FROM emp e, dept d
WHERE e.deptno = d.deptno
GROUP BY d.dname;

view of the defining principles:
1 View of complex SELECT query grammar can be used, including the linkage / team queries and subqueries;
2. In the deficiency of WITH CHECK OPTION and READ ONLY in the case, the query can not use
ORDER BY clause;
3. If there is no name for the CHECK OPTION thraldom, the system will automatically whom named, in the form of SYS_Cn;
4.OR REPLACE adoption does no delete the original view will alteration its meaning and rebuild, or re-granting thing
permission.

view query:
view is successfully created,Air Max 95, you can retrieve data from the view,Women's Air Max 2003, and from this table to retrieve the same data.
can too query and view entire the message specified in rows and columns.
such as:

retrieve data:
; SQL> SELECT * FROM dept_sum_vw;

query view definition:
; SELECT view_name, text from user_views;
which exhibits the contents of txt view defined along the SELECT expression can be won along DESC USER_VIEWS
information.

modify the view:
through OR REPLACE to re-create the same view.

DML operations above a view:
DML operation ought emulate the principle:
; 1 simple view can fulfil DML operations;
2. in the view contains a GROUP features, GROUP BY clause,Women's Air Max 2010, DISTINCT key words can not
deleted rows;
; 3 In view of these circumstances does not seem to modify the base table through view data or insert data:
a. view contains a GROUP functions, GROUP BY clause, DISTINCT keyword;
b. use statements to define col;
c.ROWNUM pseudo column.
d. base table not in view, elect the other columns defined as non-empty and no default amount.


view can be used to nourish the integrity of the database, but a limited character.
view through the implementation of referential integrity constraints in the database-level implementation constraints.

WITH CHECK OPTION clause is finite to:
through the implementation of INSERTS and UPDATES view operation can not create the view can not retrieve the data row ,
because it will insert or modify rows of data integrity constraints and perform data confirm checks.
For example:
CREATE OR REPLACE VIEW vw_emp20
AS SELECT * FROM emp
WHERE deptno = 20
; WITH CHECK OPTION constraint vw_emp20_ck;
view has been created.

results:
SELECT empno, ename, job FROM vw_emp20;

; EMPNO ENAME ; JOB
--------------------- -------------- -------------
7369 SMITH CLERK
7566 JONES MANAGER
7902 FORD ANALYST

modified:
UPDATE vw_emp20
; SET deptno = 20
; WHERE empno = 7902;
ambition produce an error:
UPDATE vw_emp20
*
ERROR in the premier line:
ORA-01402: view WITH CHECK OPTION violation

view WHERE phrase to delete:
; DROP VIEW VIEW_NAME statement to drop views.
delete the base view definition does not affect the data in the table.
merely view the owner and permissions of the user with DROP VIEW to cancel view