Views:- View can be described as virtual table which derived its data from one or more than one table columns.It is stored in the database. It is used to implements the security mechanism in the Sql Server. For example, suppose there is table called Employeeinfo whose structure is given below:-
Create table EmployeeInfo(EmpId int, EmpName nvarchar(200),EmpLogin nvarchar(20), Emppassword nvarchar(20) , EmploymentDate datetime )
And it contains the following data
EmpId EmpName EmpLogin Emppassword EmploymentDate
1 Vivek Johari Vivek VikJoh 29/01/2006
2 Virender Singh Virender Virender 06/02/2007
3 Raman Thakur Raman Raman 14/05/2007
4 Uma Dutt Sharma Uma Uma 30/03/2008
5 Ravi Kumar Thakur Ravi Ravi 30/06/2007
Now suppose that the Administrator do not want that the users have excess to the table EmployeeInfo which contains the some critical information (Emplogin, EmpPassword etc) of the Employees. So he can create a view which gives the empid, empname, employmentdate as the output and give the permission for the view to the user. In this way the administrator do not need to bother about giving the access permission for the table to the user.
The syntax for creating a View is given below:-
Create View Viewname As
Select Column1, Column2 From Tablename
Where (Condition)
Group by (Grouping Condition) having (having Condition)
For Example,
Create View View_Employeeinfo As
Select EmpId, EmpName, employmentdate
From EmployeeInfo
Now user can use the view View_EmployeeInfo as a table to get the empid , empname and employmentdate information of the employees by using the giving query
Select * from View_EmployeeInfo where empid=2
It would gives the following result
EmpId EmpName EmploymentDate
2 Virender Singh 06/02/2007
We can also use Sql Joins in the Select statement in deriving the data for the view
For Example, Suppose there is a table named EmpProjInfo which contains the information about the employee project. the structure of the EmpProjInfois given below:-
Create table EmpProjInfo (EmpId int, Projectname nvarchar(200))
and it contains the following data
EmpId Projectname
1 Abcbank
2 AtoZfinancialsol
3 learningsystem
4 ebooksystem
5 AtoZfinancialsol
Now we can create a view Vw_EmployeeProj which gives the information about the Employees and its projects
Create view Vw_EmployeeProj As
Select EmployeeInfo.EmpId, EmployeeInfo.EmpName, EmpProjInfo.Projectname from EmployeeInfo
inner join EmpProjInfo on EmployeeInfo.EmpId=EmpProjInfo.EmpId
Altering an View
If we want to alter the view, then we can use the Alter View command to alter the view
For Example,
Alter view Vw_EmployeeProj As
Select EmployeeInfo.EmpId, EmployeeInfo.EmpName, EmpProjInfo.Projectname from EmployeeInfo inner join EmpProjInfo on EmployeeInfo.EmpId=EmpProjInfo.EmpId where EmployeeInfo.EmpId in (2,3,4)
Getting Information about the Views:-
We can use the System Procedure Sp_Helptext to get the definition about the views
For example, we can use the sp_helptext command to get the information about the view Vw_EmployeeProj
sp_helptext Vw_EmployeeProj
Renaming the view:-
We can use the sp_rename system procedure to rename a view. The syntax of the sp_rename command is given below:-
SP_Rename 'Old Name', 'New name'
For example if we want to rename our view View_Employeeinfo to Vw_EmployeeInfo, we can write the sp_rename command as follows:-
sp_rename 'View_Employeeinfo', 'Vw_EmployeeInfo'
Dropping a View
We can use the Drop command to drop a view
For example, to drop the view Vw_EmployeeInfo, we can use the following statement
Drop view Vw_EmployeeInfo
Summary :-
This article tells us that view can be described as a virtual table which can derived its data from one or more than one table.We can create a view with the help of the Create View command,can alter its definition with the help of Alter view command, get its definition with the help of Sp_helptext command, rename a view with the Sp_rename command and drop a view the Drop view command.
