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Database View

View is a database object also called a logical table. it has no psychical existence. It is not like a simple table, but is a virtual or logical table which contains columns and data from different tables (may be one or more tables). A View does not contain any data, it is a set of queries that are applied to one or more tables that is stored within the database as an object. After creating a view from some table(s), it used as a reference of those tables and when executed, it shows only those data which are already mentioned in the query during the creation of the View.
Creating view Syntax:
-------------------------------------------------
CREATE VIEW [View_Name]
 AS
 [SELECT Statement]
------------------------------------ -------------
CREATE VIEW SampleView
As
SELECT EmpID, EmpName  FROM EmpInfo 
--------------------------------------------------

Data retrieve from view: 
SELECT * FROM SampleView WHERE EmpID ='FN0009C1' 
 
View does not modify. means that when we modiy as Select statement of view . we did not Alter view.
 So any changes for view , at first DROP the view and again create the view 
---------------------------------------------------
DROP VIEW SampleView  
--------------------------------------

Different types of Views

There are two different types of Views:
  • System Views
    • Information Schema View
    • Catalog View
    • Dynamic Management View (DMV)
  • User Defined Views
    • Simple View
    • Complex View
Now we discuss about Simple view and Complex View 

Simple view

A Simple View is a user defined view. A Simple View takes the data from a single table and has no function. The user defined view is created by the user as needed. We are showing a Simple View using a student table.
----------------------------------------


CREATE VIEW stud 



AS SELECT studname,studid,studaddress 

FROM student WHERE depno='d001'
  ----------------------------------------------------

Complex View


A Complex View is created for multiple tables and contains functions and group data.




CREATE VIEW [asd] 

AS 


SELECT DISTINCT depno FROM [student]




GROUP BY depno
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