What is Materialized View?

It is a one type of view which contains the result of a query.

It caches the result of complex query and you can access the result data like a normal table.

It requires physical space to store generated data. Once we put any complex query in Materialized View, we can access that query and data without disturbing a physical base table.

Only one thing you should do is: Periodically refresh your Materialized View to get newly inserted data from the base table.

In PostgreSQL, You can create a Materialized View and can refresh it.
Let me show you, full practical on this.

Create a table with sample data:

CREATE TABLE tbl_EmployeeDetails
(
    EmpID INTEGER PRIMARY KEY 
    ,EmpName VARCHAR(50)
    ,Gender CHAR(1)
    ,EmpSalary BIGINT
    ,DepartmentName VARCHAR(50)
);

INSERT INTO tbl_EmployeeDetails
VALUES 
(1,'Anvesh','M',80000,'Sales')
,(2,'Neevan','M',90000,'Sales')
,(3,'Jenny','F',50000,'Production')
,(4,'Roy','M',60000,'Production')
,(5,'Martin','M',30000,'Research')
,(6,'Mahi','F',85000,'Research')
,(7,'Kruti','F',45000,'Research')
,(8,'Manish','M',75000,'Research');

Create a materialized view to select only Male – Employee data:

CREATE MATERIALIZED VIEW vw_EmployeeMaleData_Materialized AS 
SELECT 
	EmpID
	,EmpName
	,Gender
	,EmpSalary
	,DepartmentName
FROM tbl_EmployeeDetails
WHERE Gender = 'M';

Select a data of this materialized view:

SELECT *FROM vw_EmployeeMaleData_Materialized;

Refresh a materialized view:

Once you create a materialized view, you should also refresh it otherwise newly inserted values of the table will not update in this view.

Because It acts like a physical table and once your base table update, you should refresh the data of the materialized view.

REFRESH MATERIALIZED VIEW vw_EmployeeMaleData_Materialized WITH DATA;

Create another non-materialized view to select only Male – Employee data:

CREATE VIEW vw_EmployeeMaleData_Non_Materialized AS 
SELECT 
	EmpID
	,EmpName
	,Gender
	,EmpSalary
	,DepartmentName
FROM tbl_EmployeeDetails
WHERE Gender = 'M';

Check the size of both views and find size difference between both views:
Non-Materialized view size is 0 byte and Materialized view size is around 8000 bytes because It stores the generated data.

SELECT pg_size_pretty(pg_total_relation_size('vw_EmployeeMaleData_Materialized'));
SELECT pg_size_pretty(pg_total_relation_size('vw_EmployeeMaleData_Non_Materialized'));