What Are Views in SQL?

Introduction

Structured Query Language (SQL) is the foundation of managing and manipulating relational databases. One of the most powerful features in SQL is the use of views. They simplify and compress complex queries, making database interactions more efficient and manageable. It is a must-have skill for not just data analysts, but basically anyone working with data on a daily basis. This comprehensive guide will teach you what views are and how you can create and manage them in SQL. It will also cover their benefits, types, and best practices to follow while working with them.

If you’re just starting out to explore SQL, here’s a beginner’s guide to help you: SQL For Data Science: A Beginner Guide

Overview

• Understand what a view is in SQL.
• Know the different types of views in SQL.
• Learn how to create and manage views in SQL.
• Know the benefits and best practices for using views.

What is a View in SQL?

In SQL, a view is a virtual table based on the result-set of an SQL statement. It contains rows and columns, just like a real table, but unlike a table, a view does not store data itself. Instead, it dynamically retrieves data from one or more tables as and when queried. Views are defined by SQL queries and are stored in the database metadata.

Example:

CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

Benefits of Using Views

Here are some of the benefits of using views in SQL:

1. Simplified Querying

Views can encapsulate complex joins, filters, and calculations, providing a simplified interface for users. Instead of writing intricate SQL queries, users can interact with a view that presents the data in a straightforward manner.

2. Data Security

Views can restrict access to specific rows and columns of a table. By granting users access to a view instead of the underlying tables, you can control which data they can see and modify.

3. Data Abstraction

Views provide a level of abstraction over the physical data storage. This abstraction allows changes in the underlying table structure without affecting the users’ interactions with the data through views.

4. Reusability and Maintenance

Views promote reusability of SQL code. A view can be used in multiple queries, reducing redundancy. Additionally, maintaining and updating views is easier than modifying multiple queries scattered throughout an application.

Types of Views in SQL

There are 3 types of views in SQL: simple views, complex views, and materialized views. Let’s understand each of them.

Simple Views

Simple views are formed from a single table and do not contain any group functions or complex calculations.

CREATE VIEW simple_view AS
SELECT column1, column2
FROM table_name
WHERE condition;

Complex Views

Complex views involve multiple tables, joins, and aggregation functions. They handle more sophisticated SQL logic.

CREATE VIEW complex_view AS
SELECT a.column1, b.column2, SUM(a.column3)
FROM table1 a
JOIN table2 b ON a.id = b.id
GROUP BY a.column1, b.column2;

Materialized Views

Materialized views store the result set of a query physically, unlike standard views. They are useful for improving query performance on complex and resource-intensive operations. However, materialized views require maintenance to keep them updated with changes in the underlying data.

CREATE MATERIALIZED VIEW materialized_view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

Creating and Managing Views in SQL

Now, let’s learn how to create and manage views in SQL.

Creating a View

The CREATE VIEW statement is used to define a new view. It specifies the view name and the query it is based on.

CREATE VIEW view_name AS
SELECT column1, column2
FROM table_name
WHERE condition;

Updating a View

You can use the CREATE OR REPLACE VIEW statement to update or modify an existing view. This statement allows you to redefine the view without dropping it first.

CREATE OR REPLACE VIEW view_name AS
SELECT column1, column2, column3
FROM table_name
WHERE condition;

Dropping a View

You can remove a view from the database using the DROP VIEW statement.

DROP VIEW view_name;

Refreshing a Materialized View

Materialized views need to be refreshed periodically to update their content with the latest data from the underlying tables. You can do this by using the REFRESH MATERIALIZED VIEW statement.

REFRESH MATERIALIZED VIEW materialized_view_name;

Best Practices for Using Views

Here are some best practices to follow while using views in SQL.

• Naming Conventions: Adopt clear and consistent naming conventions for views to ensure they are easily identifiable and understandable.
• Use for Read-Only Access: Limit the use of views for read-only purposes. Although updates through views are possible, they can lead to complications and unexpected behaviors.
• Indexing Underlying Tables: Ensure that the underlying tables of a view are properly indexed. This can significantly enhance the performance of queries executed on the view.
• Avoid Overcomplicating Views: While views can encapsulate complex logic, avoid creating overly complicated views. Nested views and views with extensive joins can become difficult to maintain and debug.
• Security Considerations: Use views to enhance security by restricting access to sensitive data. Ensure that users have the appropriate permissions to access only the data they need.

Conclusion

Views in SQL is a powerful tool for simplifying database interactions. It also enhances security and promotes code reusability. Knowing how to create and manage views in SQL can really help you build efficient and maintainable database solutions. Whether you’re dealing with simple queries or complex data operations, views will always be useful to streamline your SQL workflows.

Learn More: SQL: A Full Fledged Guide from Basics to Advanced Level

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K.C. Sabreena Basheer

Sabreena Basheer is an architect-turned-writer who's passionate about documenting anything that interests her. She's currently exploring the world of AI and Data Science as a Content Manager at Analytics Vidhya.