Indexed Views in SQL Server

Hello Dev, welcome to this article about indexed views in SQL Server. In this article, we will explore the concept of indexed views, how they work, how to create and use them, and their benefits. So, let’s dive in!

What are Indexed Views?

An indexed view is a database object that contains the results of a select statement, which has been optimized for efficient querying. It is similar to a regular view, but with the added benefit of having a clustered index that improves performance. Indexed views are a powerful feature of SQL Server, especially for applications that require the same data to be queried multiple times or for complex queries.

In essence, an indexed view is a precomputed query result that is stored persistently in the database. This means that the data is already calculated and stored in the view, which eliminates the need to compute the result every time the view is queried. Moreover, the clustered index on the view provides a fast and efficient way to retrieve the data, which further improves performance.

How do Indexed Views Work?

The basic idea behind indexed views is to precompute the result of a select statement and store it in a table-like structure. This table-like structure is called an indexed view, and it is created by creating a clustered index on the precomputed query result. The clustered index ensures that the data is stored in a specific order, which makes it faster to retrieve the data based on the query.

Indexed views can be used in two ways:

1. As a substitute for a table in a query.
2. As a way to cache the result of a query.

In the first case, the indexed view is used as a substitute for a table in a query. This is useful when the query involves a complex join or aggregation that is slow to execute. By using an indexed view, the precomputed result can be used instead of computing the result from scratch. This can significantly speed up the query.

In the second case, the indexed view is used as a way to cache the result of a query. This is useful when the same query is executed multiple times with different parameters. By creating an indexed view for the query result, the result can be cached and reused for each subsequent query. This can significantly reduce the query execution time.

Creating Indexed Views

Creating an indexed view is similar to creating a regular view, with the added step of creating an index on the view. The basic syntax for creating an indexed view is as follows:

CREATE VIEW	WITH SCHEMABINDING	AS
<view_name>		<select_statement>

The “WITH SCHEMABINDING” option ensures that the view is bound to the schema of the underlying tables and prevents any changes to the schema that could affect the view. This is necessary for creating an index on the view.

The next step is to create a clustered index on the view. This is done using the following syntax:

CREATE UNIQUE CLUSTERED INDEX	<index_name>	ON	<view_name>	(<column_list>)

The “CREATE UNIQUE CLUSTERED INDEX” syntax creates a clustered index on the view, which is necessary for the view to be considered an indexed view. The “index_name” is a user-defined name for the index, and the “column_list” specifies the columns to be included in the index.

Using Indexed Views

Using indexed views is similar to using regular views, with the added benefit of improved performance. When querying an indexed view, SQL Server will automatically use the clustered index on the view to retrieve the data efficiently.

However, there are some limitations to using indexed views:

• The view must be deterministic.
• The view must reference only base tables or other indexed views.
• The view cannot contain outer joins, self-joins, or subqueries.
• The view cannot use certain constructs, such as UNION or DISTINCT.
• The view cannot reference temporary tables.

Despite these limitations, indexed views are a powerful feature of SQL Server that can significantly improve performance for certain types of queries.

Benefits of Indexed Views

Indexed views offer several benefits to SQL Server users:

• Improved Query Performance: Indexed views can improve query performance by precomputing and caching the results of queries.
• Reduced Disk I/O: By using a precomputed result, indexed views reduce the amount of disk I/O needed to retrieve the data.
• Reduced CPU Utilization: By precomputing the result, indexed views reduce the amount of CPU time needed to calculate the result.
• Reduced Memory Usage: By caching the result, indexed views reduce the amount of memory needed to store the result.

Frequently Asked Questions about Indexed Views

Q1: What is the difference between a regular view and an indexed view?

A regular view is a virtual table that is based on a select statement. It does not have a physical object associated with it, and the results are calculated at runtime. An indexed view, on the other hand, is a physical object that contains the precomputed result of a select statement. It has a clustered index associated with it, which makes it faster to retrieve the data.

Q2: Can an indexed view be used to update data?

No, an indexed view is read-only. Any updates to the underlying tables must be done directly on the tables.

Q3: What are the limitations of using indexed views?

Indexed views have several limitations, including the requirement for the view to be deterministic, the restriction on using certain constructs such as UNION or DISTINCT, and the requirement for the view to reference only base tables or other indexed views.

Q4: Can an indexed view be dropped?

Yes, an indexed view can be dropped using the DROP VIEW statement.

Q5: Are indexed views supported in all versions of SQL Server?

No, indexed views were introduced in SQL Server 2000 and are supported in all later versions.

Conclusion

Indexed views are a powerful feature of SQL Server that can significantly improve query performance for certain types of queries. By precomputing and caching the results of queries, indexed views reduce disk I/O, CPU utilization, and memory usage. However, there are limitations to using indexed views, and they must be used judiciously to avoid performance issues. Overall, indexed views are a valuable tool for SQL Server users who need to improve query performance.