PostgreSQL Materialized Views: Syntax & Query Examples| A 101 Guide

on Database Management Systems, PostgreSQL, PostgreSQL Materialized Views, Tutorials • July 8th, 2022 • Write for Hevo

PostgreSQL Materialized Views_FI

If you’re using PostgreSQL to meet your database needs, you’ve probably seen some process disruptions while implementing manual and repetitive tasks.

Executing the same expensive queries on a regular basis keeps eating up a lot of your time and energy. This is where the concept of PostgreSQL Materialized Views comes into the picture.

A PostgreSQL Materialized View is a database object that saves the result of a previously computed database query and allows you to easily refresh it as needed.

In this article, you will gain information about PostgreSQL Materialized Views. You will also gain a holistic understanding of PostgreSQL, its key features, and different statements, syntax, and examples associated with implementing PostgreSQL Materialized Views.

Read along to find out in-depth information about creating PostgreSQL Materialized Views.

Table of Contents

What is PostgreSQL?

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PostgreSQL is an open-source relational database. It is famous for its Open-Source platform, which supports all RDBMS functionalities. In addition to RDBMS capabilities, it provides indexes, views, stored procedures, triggers, atomicity features, and so on. SQL and JSON queries are also supported. PostgreSQL is also capable of serving as a data warehouse system.

PostgreSQL is compatible with a wide range of operating systems, including Windows, Linux, macOS, and UNIX. The source code for PostgreSQL is publicly accessible under an open-source license, letting users use, modify, and implement it as needed. Since PostgreSQL offers no license costs, there is no risk of over-deployment, which saves a lot of expenses.

Before having any information about PostgreSQL Materialized Views, you can have a brief idea about PostgreSQL Tables.

Key Features of PostgreSQL

Some of the key features of PostgreSQL are as follows:

  • Customizable: PostgreSQL can be altered and customized by writing plugins to make the DBMS meet your needs. It also lets you integrate custom functions written in other programming languages like Java, C, C++, and others.
  • Community Support: A professional community is always available to its users. PostgreSQL also has a large range of private, third-party support services available.
  • Open-Source: As a free and open-source solution, PostgreSQL offers Object-Oriented and Relational Database capabilities.
  • Users: It is a well-known and commonly used RDBMS. Apple, Etsy, Facebook, Instagram, Red Hat, Skype, Spotify, and many other companies utilize PostgreSQL.
  • Code quality: Every line of code in PostgreSQL is evaluated by a team of professionals, and the whole development process is driven by the community, allowing for speedy bug reporting, changes, and verification.
  • Data Availability and Resiliency: PostgreSQL versions that are privately supported provide additional high availability, resilience, and security for mission-critical production settings such as government agencies, financial institutions, and healthcare providers.

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What are PostgreSQL Materialized Views?

According to the official documentation of PostgreSQL, “Materialized views in PostgreSQL use the rule system like views do, but persist the results in a table-like form.

Views, as we know, are virtual tables that reflect data from underlying tables. In PostgreSQL, a view can be accessible as a virtual table. In other words, a PostgreSQL view is a logical table that uses a SELECT statement to represent data from one or more underlying tables. In reality, they don’t hold data physically.

However, in PostgreSQL, only particular Views are permitted to physically store data. These are referred to as PostgreSQL Materialized Views. Materialized views store the result of a comprehensive and expensive query and enable you to update & refresh it on a regular basis.

Advantages of using PostgreSQL Materialized Views

Some of the advantages associated with using PostgreSQL Materialized Views are as follows:

  • A PostgreSQL Materialized View is particularly efficient at query execution. The data of those views are physically saved and you don’t need to read all of the data associated with a query every time.
  • These Views make complicated data easier to understand by reducing query information. It will save you time from writing that query over and again whenever you want data specific to that query. Thus, it helps you improve your performance.
  • Materialized Views also help developers in cutting costs.
  • When it comes to querying large databases, PostgreSQL Materialized View will substantially increase the speed of the computations.

How to implement PostgreSQL Materialized Views?

Different functions associated with the implementation of PostgreSQL Materialized Views are as follows:

1) Create PostgreSQL Materialized Views

You can create a PostgreSQL Materialized View by using the CREATE MATERIALIZED VIEW statement.

A) Syntax

According to the PostgreSQL Documentation, the syntax is as follows:

CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] table_name
    [ (column_name [, ...] ) ]
    [ USING method ]
    [ WITH ( storage_parameter [= value] [, ... ] ) ]
    [ TABLESPACE tablespace_name ]
    AS query
    [ WITH [ NO ] DATA ];

B) Description

The description of the above syntax goes like this:

  • IF EXISTS specifies not to throw an error if a PostgreSQL materialized view with the same name already exists. A notice is issued in this case.
  • table_name represents the name of the PostgreSQL materialized view that you’re going to create. You need to specify the name of the PostgreSQL materialized view after the “CREATE MATERIALIZED VIEW” statement.
  • column_name specifies the name of any column in the new PostgreSQL Materialized view you have created. However, this is optional. If you don’t apply any of the names of the columns then it carries forward the output column names of the query.
  • USING method is an optional clause that defines the table access method that will be used to store the contents of the new materialized view. The access method must be of type TABLE. If this method is not mentioned then the new PostgreSQL Materialized View takes the default table access method.
  • WITH ( storage_parameter [= value] [, … ] ) clause is used to specify any optional storage parameters for the PostgreSQL Materialized view to be created.
  • tablespace_name represents the name of the tablespace where the new PostgreSQL Materialized View is to be created. You need to specify the tablespace name after the TABLESPACE keyword. However, this parameter is optional and if not specified, the default_tablespace will be consulted.
  • query here represents the query that you will be writing to get the data from the underlying tables for creating the PostgreSQL Materialized View. You need to write the query after the “AS” keyword.
  • If you want to load data into the PostgreSQL Materialized View during the time of its creation, you can write WITH DATA after the query; otherwise, you can write WITH NO DATA. The view is marked as unreadable if you use WITH NO DATA. It implies you won’t be able to query data from the view until you’ve loaded data into it. By default, if you don’t write anything then views are automatically refreshed. You can change this by using WITH NO DATA.

3) Examples

An example of creating a PostgreSQL Materialized View according to postgresqltutorials.com is as follows: 

CREATE MATERIALIZED VIEW rental_by_category
AS
 SELECT c.name AS category,
    sum(p.amount) AS total_sales
   FROM (((((payment p
     JOIN rental r ON ((p.rental_id = r.rental_id)))
     JOIN inventory i ON ((r.inventory_id = i.inventory_id)))
     JOIN film f ON ((i.film_id = f.film_id)))
     JOIN film_category fc ON ((f.film_id = fc.film_id)))
     JOIN category c ON ((fc.category_id = c.category_id)))
  GROUP BY c.name
  ORDER BY sum(p.amount) DESC
WITH NO DATA;

2) Refresh PostgreSQL Materialized Views

You can replace the contents of a PostgreSQL Materialized View by using the REFRESH MATERIALIZED VIEW statement.

A) Syntax

According to the PostgreSQL Documentation, the syntax is as follows:

REFRESH MATERIALIZED VIEW [ CONCURRENTLY ] name
    [ WITH [ NO ] DATA ]

B) Description

The description of the above syntax goes like this:

  • When you refresh data for a materialized view, PostgreSQL locks the entire table, making it impossible to query. You can avoid this by using the CONCURRENTLY option. This is optional. You can mention CONCURRENTLY after the REFRESH MATERIALIZED VIEW statement.
  • name represents the name of the PostgreSQL materialized view that you’re going to refresh. 
  • If WITH DATA is mentioned, the backing query is executed to deliver the new data, and the PostgreSQL Materialized view is scannable in this case. If WITH NO DATA is mentioned no new data is created and the materialized view remains unscannable. By default, PostgreSQL takes WITH DATA into consideration. (CONCURRENTLY and WITH NO DATA cannot be specified together).

C) Examples

Some of the examples which showcase the use case of Refreshing PostgreSQL Materialized Views are as follows:

1) Replacing contents of the Materialized view and leaving it in a scannable state:

REFRESH MATERIALIZED VIEW order_summary;

2) Command to free storage of the Materialized view and leave it in an unscannable state:

REFRESH MATERIALIZED VIEW annual_statistics_basis WITH NO DATA;

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3) Drop PostgreSQL Materialized Views

You can remove an existing PostgreSQL Materialized View by using the DROP MATERIALIZED VIEW statement.

A) Syntax

According to the PostgreSQL Documentation, the syntax is as follows:

DROP MATERIALIZED VIEW [ IF EXISTS ] name [, ...] [ CASCADE | RESTRICT ]

B) Description

The description of the above syntax goes like this:

  • IF EXISTS specifies not to throw an error if a PostgreSQL materialized view with the same name already exists. A notice is issued in this case. This is optional.
  • name represents the name of the PostgreSQL Materialized view that you’re going to remove. 
  • CASCADE option is used to automatically drop any object that is dependent on the PostgreSQL Materialized View that is being removed and in turn remove all those objects that depend on those objects as well. The RESTRICT option explicitly helps to stop dropping the PostgreSQL Materialized View if any objects are dependent on it. If nothing is specified, then RESTRICT is considered by default.

C) Examples

An example that showcases the usage of dropping PostgreSQL Materialized Views is as follows:

DROP MATERIALIZED VIEW order_summary;

Conclusion

In this article, you learned about PostgreSQL Materialized Views and their advantages. This article also focused on PostgreSQL, its key features, and different statements, syntax, and examples associated with implementing PostgreSQL Materialized Views.

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