You can create Views with all columns or selected columns from base table. If column names are not specified, View inherits the same columns from the base table.

--Creating view with all columns from base table

CREATE OR REPLACE VIEW vw_dept
AS 
SELECT * FROM Dept;

View created.


--Accessing view data
SELECT * FROM vw_dept;

   DEPTNO  DNAME          LOC
---------- -------------- -------------
        10 ACCOUNTING     NEW YORK
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON

FORCE Views

View being a schema object is stored within the database either in valid state or in invalid state. View can operate in any SQL query only when it is in valid state. The invalid state view can’t be referred in operational logic, but stay in the database as forced views. As soon as the basic requirements of this view are fulfilled, the view automatically goes into valid state.

SELECT * FROM Dept_force;
SELECT * FROM Dept_force
              *
ERROR at line 1:
ORA-00942: table or view does not exist


--Force view creation when base table doesn't exist

CREATE OR REPLACE FORCE VIEW vw_dept_force
AS 
SELECT * FROM Dept_force;

Warning: View created with compilation errors.


--Accessing force view
SELECT * FROM vw_dept_force;
SELECT * FROM vw_dept_force
              *
ERROR at line 1:
ORA-04063: view "SCOTT.VW_DEPT_FORCE" has errors

If columns are declared with double quotes during table or view creation, then column names become case sensitive. In that case you have to follow the exact casing that is used during column declaration in the CREATE statement else it produces error.

--Error! Double quotes preserves the case of the identifier

SELECT "Employee id", Name, Designation
  FROM Employees
 WHERE "Base Salary" > 1500;
SELECT "Employee id", Name, Designation
       *
ERROR at line 1:
ORA-00904: "Employee id": invalid identifier


--Using proper case using double quotes

SELECT "Employee ID", Name, Designation
  FROM Employees
 WHERE "Base Salary" > 1500;