Views in SQL Server

Introduction

 

In this article, we are going to discuss the Views in the SQL server. It is one of the important elements in the SQL server; it eliminates the difficulties in the business process. There are lots of significant improvements in the view, especially in the SQL server. They have introduced the indexed views and INSTEAD of Trigger on the permanent view. Let us discuss the views with more practical way.

 

Views in SQL Server

 

The view is a virtual table, which can have multiple columns from the one or more table. It can be used as the normal table. Normally view cannot store the data permanently in the table. When we create the view it stores the view definition schema as object under the concerned database.

 

Let us see the syntax of the create view

 

CREATE VIEW View Name [Alias name1, name2,]

WITH ENCRYPTION

WITH SCHEMA BINDING

AS

SELECT statement [WITH CHECK OPTION]

 

The create view can be created with the view name and the alias can be given in the view name parameter parenthesis. The view schema can be stored in the encrypted format. Here is an option like SCHEMA BINDING; this is an important milestone in the view to allow the developers to create a permanent view.

 

When to use VIEW?

 

When you have complex queries, that use many places in the stored procedures or functions, etc..,

 

It will be used as a security mechanism in web applications. When we use the original table in the web applications the hackers may drop the table. That time the original data will persist in the table.

 

When you want to hide the particular columns to the specific people then we can create a specialized view.

 

Encrypted View in SQL Server

 

The definition of the schema will be encrypted and stored as object in the database. This can be done using the ENCRYPTION option in the view creation.

IF OBJECT_ID('[DBO].Vw_SqlObjects_Encrypted') IS NOT NULL
BEGIN
   DROP VIEW [DBO].Vw_SqlObjects_Encrypted
   PRINT '<< [DBO].Vw_SqlObjects_Encrypted View dropped >>'
END
GO
CREATE VIEW [DBO].Vw_SqlObjects_Encrypted
WITH ENCRYPTION
AS
   SELECT
       O.Object_ID
      ,O.Name
      ,'Type' = CASE O.type WHEN 'S' THEN 'Scalar Functions'
                          WHEN 'F' THEN 'Functions'
                          WHEN 'V' THEN 'Views'
                          WHEN 'PK' THEN 'Primary keys'
                          WHEN 'TR' THEN 'Triggers'
                          WHEN 'P' THEN 'Procedures'
                          WHEN 'U' THEN 'User Defined Functions'
                          WHEN 'TF' THEN 'Table Valued Functions'
                          WHEN 'IF' THEN 'Inline Functions' END
      ,O.create_date
      ,O.modify_date
      ,CASE WHEN SC.encrypted = 0 THEN 'No' ELSE 'Yes' END AS [IsEncrypted]
      ,SC.text
  FROM
      SYS.OBJECTS O
  INNER JOIN
      SYSCOMMENTS SC ON SC.id = O.object_id
 GO
IF OBJECT_ID('[DBO].Vw_SqlObjects_Encrypted') IS NOT NULL
BEGIN
   PRINT '<< [DBO].Vw_SqlObjects_Encrypted View created >>'
END
GO

Now if you want to see the view schema definition for the above view is not possible. We have stored in the encrypted format. This is a significant option to hide the important calculations inside the view from the others.

 

In case of any alter in the view must be stored externally somewhere else.

SELECT text FROM SYSCOMMENTS WHERE id = OBJECT_ID('[DBO].Vw_SqlObjects_Encrypted')
SELECT definition FROM SYS.sql_modules WHERE object_id = OBJECT_ID('[DBO].Vw_SqlObjects_Encrypted')

sp_helptext Vw_SqlObjects_Encrypted

If you execute the above queries then it will say like view is encrypted.

 

There are three types of views in the SQL server.

 

They are 

1. Normal or Standard view
2. Indexed or permanent view
3. Partitioned view

Normal or Standard view

 

This view is most frequently used by the developers. When creating the view the schema will be stored an object in the database. When we retrieve the content from this virtual table, it will be executed the schema and stored the data from the parent table.

 

Here if you have the result from the same table then it can be updated and inserted. The deleted row will be reflected in the original table.

USE [Northwind]
GO
IF OBJECT_ID('[DBO].vw_ViewProducts','V') IS NOT NULL
BEGIN
  DROP VIEW [DBO].vw_ViewProducts
  PRINT '<< [DBO].vw_ViewProducts view dropped.. >>'
END
GO
CREATE VIEW [DBO].vw_ViewProducts
AS
 SELECT
    ProductID,ProductName,SupplierID,CategoryID,QuantityPerUnit,UnitPrice,UnitsInStock,
UnitsOnOrder,ReorderLevel,Discontinued
 FROM Products
GO
IF OBJECT_ID('[DBO].vw_ViewProducts','V') IS NOT NULL
BEGIN
  PRINT '<< [DBO].vw_ViewProducts view created.. >>'
END
GO
--O/P
SELECT * FROM [DBO].vw_ViewProducts
--INSERT
INSERT INTO [DBO].vw_ViewProducts(ProductName,SupplierID,CategoryID,QuantityPerUnit,UnitPrice,
UnitsInStock,UnitsOnOrder,ReorderLevel,Discontinued)
VALUES('Test View',1,2,'100 per bag',25.45,89,57,15,0)
--DELETE
DELETE FROM [DBO].vw_ViewProducts WHERE ProductID = 81

Here you can do the DML operations in the view when you have only one table.

 

Indexed views

 

The indexed or permanent view is one of the new features introduced in the SQL server. We have seen that the view only store the schema definition and it will get execute and load the data into the virtual table at the time of view used. But this view creates the permanent view and we can create the indexes on the table. It allows us to create the instead of trigger.

 

The indexed view can be created with the WITH SCHEMA BINDING option while creating the view.

 

The indexed view has some restrictions like cannot use the TOP, DISTINCT, UNION, ORDER BY and aggregate functions.

 

It allows us to use the GROUP BY statement but we cannot use COUNT statement. Instead of that COUNT_BIG statement can be used.

IF EXISTS(SELECT OBJECT_ID FROM SYS.OBJECTS WHERE OBJECT_ID = OBJECT_ID(N'[DBO].Vw_Product_Sales_Report',N'V'))
BEGIN
  DROP VIEW [DBO].Vw_Product_Sales_Report
  PRINT '<< [DBO].Vw_Product_Sales_Report view dropped >>'
END
GO
CREATE VIEW [DBO].Vw_Product_Sales_Report
WITH SCHEMABINDING
AS
  SELECT
      O.OrderID
     ,C.CustomerID
     ,C.CompanyName
     ,C.Address+', '+C.City AS [Customer Address]
     ,OD.ProductID
     ,P.ProductName
     ,OD.UnitPrice
     ,OD.Quantity
     ,(OD.UnitPrice * OD.Quantity) AS [Total]
     ,(OD.UnitPrice * OD.Quantity) * OD.Discount/100 AS [Discount]
   FROM
     [DBO].Orders O (NOLOCK)
   INNER JOIN [DBO]."Order Details" OD (NOLOCK) ON OD.OrderID = O.OrderID
   INNER JOIN [DBO].Customers C (NOLOCK) ON C.CustomerID = O.CustomerID
   INNER JOIN [DBO].Products P (NOLOCK) ON P.ProductID = OD.ProductID
GO
IF EXISTS(SELECT OBJECT_ID FROM SYS.OBJECTS WHERE OBJECT_ID = OBJECT_ID(N'[DBO].Vw_Product_Sales_Report',N'V'))
BEGIN
  PRINT '<< [DBO].Vw_Product_Sales_Report view created >>'
END
GO

Here the indexed view has created. When you retrieve the data from this table, it will execute like normal table.

 

There are some restrictions while creating this indexed view like the name of the view must be two part name and we cannot use select * in the view schema definition.

 

Normally view cannot have the triggers but from the SQL server onwards We can create the Instead of trigger on the instead of trigger.

 

Partitioned Views

 

The partitioned view and its execution is like normal view. It will work across the database and across the server.

 

There are two types of Partitioned views. They are 

1. Local Partitioned View
2. Global Partitioned View

1. Local Partitioned View

 

The local partitioned view can be created within same server but different database.

 

The view schema definition will be stored in the executed database. But when we try to retrieve the data from the table, it has to execute the schema definition internally and load the data.

 

Let us see an example.

USE [Northwind]
GO
CREATE TABLE EmployeeList
(
  iEmployeeID INT IDENTITY(1,1),
  vFirstName VARCHAR(25) NOT NULL,
  vLastName VARCHAR(25) NOT NULL,
  iDeptID INT,
  vAddress VARCHAR(25) NOT NULL,
  vCity VARCHAR(25) NOT NULL,
  vState VARCHAR(25) NOT NULL,
  vCountry VARCHAR(25) NOT NULL,
)
GO
USE [Master]
GO
CREATE TABLE Department
(
  iDeptID INT IDENTITY(1,1) PRIMARY KEY,
  vDeptName VARCHAR(50),
  vDeptDesc VARCHAR(25),
  vDeptAddedBy VARCHAR(50),
  vPostedDate DATETIME DEFAULT GETDATE()
)
GO
--SELECT * FROM Department
USE [Northwind]
GO
IF OBJECT_ID('[DBO].vw_LocalPartion_View','V') IS NOT NULL
BEGIN
  DROP VIEW [DBO].vw_LocalPartion_View
  PRINT '[DBO].vw_LocalPartion_View view dropped...'
END
GO
CREATE VIEW [DBO].vw_LocalPartion_View
AS
SELECT E.iEmployeeID,E.vFirstName+SPACE(1)+E.vLastName AS [Name],
       D.vDeptName,E.vAddress,E.vCity,E.vState
FROM EmployeeList E
--INNER JOIN Master..Department D ON D.iDeptID = E.iDeptID --Either one of the way will be used.
INNER JOIN Master.dbo.Department D ON D.iDeptID = E.iDeptID
GO
IF OBJECT_ID('[DBO].vw_LocalPartion_View','V') IS NOT NULL
BEGIN
  PRINT '[DBO].vw_LocalPartion_View view created...'
END
GO
--O/p
SELECT * FROM [DBO].vw_LocalPartion_View

2. Global Partitioned View

 

The global Partitioned view will work across the server. The view can be created to join the table across the server.

 

The accessing format will be like this.

 

[Server Name].  Database Name. Table Name

 

When we execute the view if it is not linked with the current server then it will ask us to link the external server.

 

The following system stored procedure will be used to link the server.

sp_addlinkedserver 'Server name'

The following system catalog table is used to see the list of linked servers.

SELECT * FROM SYS.SERVERS

INSTEAD OF Triggers on the Indexed View

 

Normally the triggers cannot be created on the view. But SQL server onwards we can create the INSTEAD OF trigger on the indexed views.

USE [Northwind]
GO
IF OBJECT_ID('[DBO].[VW_Trigger_Example') IS NOT NULL
BEGIN
   DROP VIEW [DBO].[VW_Trigger_Example]
   PRINT '[DBO].[VW_Trigger_Example view dropped..'
END
GO
CREATE VIEW [DBO].[VW_Trigger_Example]
WITH SCHEMABINDING
AS
  SELECT P.ProductID,P.ProductName,P.SupplierID,
         OD.OrderID,OD.UnitPrice,OD.Quantity
  FROM [DBO].Products P
  INNER JOIN [DBO].[Order Details] OD ON OD.ProductID = P.ProductID
GO
IF OBJECT_ID('[DBO].[VW_Trigger_Example') IS NOT NULL
BEGIN
   PRINT '[DBO].[VW_Trigger_Example view created..'
END
GO
--SELECT * FROM VW_Trigger_Example
IF OBJECT_ID('[DBO].Tr_Delete_TriggerExample','TR') IS NOT NULL
BEGIN
  DROP TRIGGER [DBO].Tr_Delete_TriggerExample
  PRINT '[DBO].Tr_Delete_TriggerExample trigger dropped..'
END
GO
CREATE TRIGGER [DBO].Tr_Delete_TriggerExample
ON [DBO].VW_Trigger_Example
INSTEAD OF DELETE
AS
BEGIN
   PRINT '----------------------------------------'
   PRINT 'This is an example of INSTEAD OF Trigger'
   PRINT '----------------------------------------'
   SELECT TOP 1 * FROM DELETED
END
GO
IF OBJECT_ID('[DBO].Tr_Delete_TriggerExample','TR') IS NOT NULL
BEGIN
  PRINT '[DBO].Tr_Delete_TriggerExample trigger created..'
END
GO
--O/P
--SELECT * FROM [DBO].[VW_Trigger_Example] WHERE ProductID = 11
DELETE FROM [DBO].[VW_Trigger_Example] WHERE ProductID=11

How to view the Created Views?

 

There are few ways to view the schema definition of the created views.

SP_HELPTEXT vw_LocalPartion_View
SELECT id,text FROM SYSCOMMENTS WHERE id = OBJECT_ID('[DBO].vw_LocalPartion_View')
SELECT object_id,definition FROM SYS.SQL_MODULES WHERE OBJECT_ID = OBJECT_ID('[DBO].vw_LocalPartion_View')

How to drop the View in SQL Server?

 

If you want to drop the view then you can use the following statement. When you drop the table underlying view will not be deleted. But if you run that view it will throw an error.

 

DROP VIEW VIEW_NAME

 

How to alter the view in SQL Server?

 

If you want to do changes in the created views then you can alter the view whatever you want to view the same view name.

 

ALTER VIEW VIEW_NAME

AS

SELECT [Columns List]....

 

Conclusion

 

So far, we have seen the views in the SQL server. I hope that this has given enough idea about the views. If there is any correction or suggestions about this article please post your feedback.