Views in SQL Server are a powerful tool that allow you to create virtual tables based on the data from one or more underlying tables. They provide a way to simplify complex queries and encapsulate logic for easier data retrieval. However, there are certain limitations and misconceptions when it comes to using indexes on views.

One common misconception is that creating an index on a view will automatically improve performance by reducing the load on the original table. However, this is not always the case. In fact, the view may not utilize the index created on it and instead use the index on the underlying table.

Let’s consider an example to illustrate this. We start by creating a base table and then create a view on top of it. We also create an index on the view. Subsequently, we run a simple SELECT statement on both the base table and the view.

USE tempdb
GO

-- Create SampleTable
CREATE TABLE mySampleTable (ID1 INT, ID2 INT, SomeData VARCHAR(100))
INSERT INTO mySampleTable (ID1,ID2,SomeData)
SELECT TOP 100000 ROW_NUMBER() OVER (ORDER BY o1.name),
ROW_NUMBER() OVER (ORDER BY o2.name),
o2.name
FROM sys.all_objects o1
CROSS JOIN sys.all_objects o2

-- Create Index on Table
CREATE UNIQUE CLUSTERED INDEX [IX_OriginalTable] ON mySampleTable (ID1 ASC)

-- Select from table
SELECT ID1,ID2,SomeData
FROM mySampleTable

-- Create View
CREATE VIEW SampleView
WITH SCHEMABINDING
AS
SELECT ID1,ID2,SomeData
FROM dbo.mySampleTable

-- Create Index on View
CREATE UNIQUE CLUSTERED INDEX [IX_ViewSample] ON [dbo].[SampleView] (ID2 ASC)

-- Select from view
SELECT ID1,ID2,SomeData
FROM SampleView

Upon observing the execution plan and the use of indexes along with the queries, we notice that the view uses the same index as the original table and does not utilize the index created on the view. This is because the optimizer determines that the original index will be more beneficial in the query plan than the newly created index.

If you want the view to act as an independent table and have no relation with the original underlying table, you can use the hint [noexpand]. This will prevent the view from expanding and using the index on the base table.

It’s important to understand that the usage of indexes in views depends on various factors such as the complexity of the query, the size of the data, and the distribution of the data. It’s recommended to analyze the execution plans and perform thorough testing to determine the most efficient indexing strategy for your views.

In conclusion, while creating an index on a view may seem like a straightforward way to improve performance, it’s essential to understand how SQL Server utilizes indexes in views. By analyzing execution plans and considering the specific requirements of your queries, you can optimize the indexing strategy for your views and achieve better performance.

Stay tuned for future articles where we will explore more limitations and best practices when working with SQL Server views.