Adventures in Machine Learning

Optimizing SQL Databases with Indexes on Computed Columns

When it comes to optimizing SQL databases, indexing is a critical component. Indexes, in essence, serve as pointers to the data, speeding up query execution time and improving overall performance.

There are various types of indexes, including unique, clustered, non-clustered, and filtered indexes. In this article, we will focus on indexes on computed columns, exploring how to create them, their requirements, and benefits.

Indexes on Computed Columns

In SQL, computed columns are columns that are not stored physically in the database but are computed or derived using an expression or a function. These computed columns are useful in situations where data needs to be analyzed or presented in a particular way.

For instance, you may need to calculate a customer’s age from their date of birth, or concatenate a customer’s first name and last name to get their full name.

1. Steps for Creating Indexes on Computed Columns

To create an index on a computed column, follow these steps:

  • Define the computed column using an expression or function
  • Create a non-computed column with the same schema as the computed column
  • Create an index on the non-computed column

For example, let us consider the following scenario where we have a Customers table with columns such as id, first_name, last_name, and date_of_birth. Suppose we want to create an index on the computed column ‘age,’ which is derived from the date_of_birth column, using the DATEDIFF function.

Here are the steps we would take:

  • Create the computed column:
    ALTER TABLE Customers
    ADD age AS DATEDIFF(YEAR, date_of_birth, GETDATE())
  • Create a non-computed column with the same schema as the computed column:
    ALTER TABLE Customers
    ADD age_non_computed INT
  • Update the non-computed column with the computed column’s value:
    UPDATE Customers
    SET age_non_computed = age
  • Create an index on the non-computed column:
    CREATE INDEX age_index ON Customers(age_non_computed)

2. Benefits of Indexes on Computed Columns

Indexes on computed columns offer several benefits, such as improved query performance, reduced storage requirements, and improved search capabilities.

  • Improved Query Performance: Indexes on computed columns can speed up the execution time of queries as they make it easier for the database engine to search and retrieve data. In addition, computed columns can be used to filter, sort, or group data, which can further speed up query execution.
  • Reduced Storage Requirements: Computed columns are not physically stored in the database; instead, they are derived from other columns and are computed during query execution. This means that you do not need to store redundant data, reducing storage requirements.
  • Improved Search Capabilities: Computed columns can be used to create full-text indexes, which allow for complex searches across multiple columns. Additionally, computed columns can be used to improve search ranking algorithms or to enable advanced text mining and analytical capabilities.

3. Requirements for Creating Indexes on Computed Columns

Creating an index on a computed column has some requirements that must be met to ensure optimal performance:

  • Deterministic Functions: When defining a computed column, you must use a deterministic function.
  • Persistence: Non-computed columns that have the same schema as the computed column need to be persistent, meaning that they must be stored physically in the database.
  • Storage Capacity: Computed columns can require a lot of storage space, which can affect database performance.

It is crucial to consider the storage capacity of your database before creating computed columns.

Querying the Sales.Customers Table

The Sales.Customers table is an essential component of most SQL databases.

It stores information about customers, such as their names, addresses, and contact details. When querying the Sales.Customers table, it is crucial to optimize the query execution plan to avoid slow performance.

Here are some tips on how to query the Sales.Customers table efficiently:

  1. Use Appropriate Indexes
  2. Use the Appropriate Data Type
  3. Use Appropriate Joins

Inefficient Query Execution Plan of Sales.Customers Table

Despite the above measures, it is still possible to create inefficient query execution plans when querying the Sales.Customers table.

Some of the common causes of inefficient query execution include:

  • Not Using Indexes: Failure to use indexes can significantly slow down query execution. If you are not sure which indexes to use, use the database tuning advisor to recommend appropriate indexes.
  • Overuse of Joins: Querying multiple tables that require multiple joins can slow down the query execution plan. Consider denormalizing the tables or using materialized views to improve performance.
  • Using Suboptimal Queries: Using suboptimal queries, such as using wildcard characters unnecessarily or not using the appropriate data types, can slow down query execution.


Optimizing SQL database performance is key to providing fast and efficient data retrieval. When creating indexes on computed columns, it is essential to ensure that they meet the required specifications.

Additionally, querying the Sales.Customers table requires the appropriate use of indexes, data types, and joins to avoid an inefficient query execution plan. By following the steps outlined in this article, you can create efficient query execution plans and improve overall performance.

3. Oracle and PostgreSQL Indexes

In the world of relational databases, Oracle and PostgreSQL are two popular choices for enterprises.

Both of these database management systems offer indexing capabilities to expedite data retrieval and enhance performance. However, the mechanisms for indexing differ between these two platforms.

1. Overview of Oracle and PostgreSQL Indexes

Oracle and PostgreSQL employ different methodologies for indexing data, each with its own advantages and disadvantages.

Oracle uses the B-tree index, which is a hierarchical tree data structure that allows rapid access to data. B-tree indexes are appropriate for large tables that contain many columns.

On the other hand, PostgreSQL uses multiple indexing methods, including B-tree, Hash, GIN (Generalized Inverted Index), and GiST (Generalized Search Tree). Each indexing method provides unique benefits for different applications.

2. Function-Based Indexes for Oracle and Expression-Based Indexes for PostgreSQL

Oracle and PostgreSQL offer unique indexing methods when it comes to computed columns.

Function-based indexes are predominant in Oracle. These indexes allow users to create an index on a computed column by specifying a function that computes the value of the column.

Expression-based indexes are predominant in PostgreSQL. They are used for indexing computed columns, where an index is created on an expression involving one or more columns.

For example, a function-based index could be created to compute the age of a customer from their date of birth, as shown in the following Oracle SQL code:


In PostgreSQL, the following code would create an expression-based index for the same purpose:

CREATE INDEX age_idx ON customers ((EXTRACT(year FROM age(current_date, dob))));

3. Similar Effects of Indexes on Computed Columns in SQL Server

Creating indexes on computed columns can provide similar benefits across different relational database management systems.

In SQL Server, creating an index for a computed column can speed up query performance and reduce storage requirements, just like in Oracle and PostgreSQL. Although SQL Server uses different mechanisms, the underlying principle of indexed computed columns can be applied across different database platforms.

4. Creating an Index on Email_Local_Part Column

Email addresses are a common aspect of many applications and databases.

In particular, the email_local_part column can be used to optimize searches for emails based on names, locations, and other terms. Creating an index on the email_local_part column can result in a significant improvement in query performance.

1. Creating a Computed Column Based on Email_Local_Part Expression

In order to create an index on a computed column, it is necessary to first create the computed column.

The computed column for the email_local_part can be created using regular expression pattern matching. For example, the following SQL code will create a computed column called email_local_part:

ALTER TABLE customer ADD email_local_part AS (regexp_substr(email, '^([^@]+)@'));

This code uses a regular expression that captures the characters before the “@” symbol in an email address.

When coupled with the AS keyword, the code will create a new column called email_local_part that can be indexed.

2. Creating a Nonclustered Index for Email_Local_Part Column

Creating an index on the email_local_part column can further improve search performance. A nonclustered index can be added by the following SQL code:

ON customer (email_local_part)

This index provides a quick reference to the email_local_part column in the table, which can speed up searches and reduce query times.

3. Using Email_Local_Part Column in Querying

Once the computed column has been created and the index has been added, querying the table for email addresses becomes much more efficient. Users can quickly search for customer email addresses based on their local part.

For instance, the following SQL code can be used to search all customer email addresses with a specific local part:

SELECT * FROM customer 
WHERE email_local_part = 'alex'

This code returns all customer records which have the local part “alex” in their email address.


Indexes on computed columns can significantly improve database query performance and reduce storage requirements. While the underlying mechanisms for indexing differ across database management systems, the benefits of indexed computed columns are universal.

Creating an index on the email_local_part column of customers can be particularly useful for searching customer emails based on local parts, allowing faster, more targeted queries that are critical for business success.

5. Requirements for Indexes on Computed Columns

Creating indexes on computed columns is a powerful way to optimize performance in databases. However, to create these indexes, certain requirements must be met to avoid problems and misunderstandings.

Here are some of the key requirements to consider when creating indexes on computed columns:

  1. Same Owner for Computed Column Expression
  2. Deterministic Computed Column Expression
  3. Precise Computed Column Expression
  4. Data Types for Computed Column Expression Result
  5. ANSI_NULLS Option and Other Option Settings

Overall, creating indexes on computed columns requires careful consideration and planning.

By meeting these requirements, it is possible to create efficient and effective indexed computed columns that can dramatically improve database performance.

In conclusion, indexes on computed columns offer an effective way to optimize query performance in databases.

However, fulfilling the requirements listed above is critical in ensuring error-free data handling and successful indexing. A good understanding of these requirements, coupled with best practices in computed column creation, can help developers to create an index that ensures a stable foundation for optimized query performance and faster database execution times.

In summary, creating indexes on computed columns is essential for optimizing database performance and speeding up query execution. There are several critical requirements that developers must comply with to ensure accuracy and avoid errors in index creation.

These requirements include the same owner of the computed column expression, precise and deterministic computed column expression, valid data types for the computed column expression result, ANSI_NULLS option settings, and other option settings. Careful adherence to these requirements will help developers create effective indexed computed columns that deliver optimal performance when handling data.

As a takeaway, it’s important to keep these requirements in mind when creating indexed computed columns in any RDBMS’ design and maintenance to achieve fast and efficient data retrieval.

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