In my previous article I have given the examples of materialized views in oracle. I will focus on PostgreSQL Materialized View with multiple real life examples. But before that the question in users mind is what is Postgres Materialized View and what is its use? The materialized view is nothing but the view like structure in database but data is stored physically in the memory so that user can retrieve data as fast as possible.
Why to use PostgreSQL Materialized View ?
Everybody has question in mind that why do we need to use materialized view. The answer is in one line- to improve the performance of the query. In day to day life programmer deals with multiple complex sql queries. User needs to refresh materialized views on timely basis to retrieve data in it.
Syntax of Materialized View :
CREATE MATERIALIZED VIEW View_Name
AS Select Query
With Data / No Data;
The above syntax is used to create materialized view in PostgreSQL.The materialized views are key objects which we is used to improve the performance of application.There are two options of creating materialized views :
- Create Materialized view with data .
- Create Materialized view without data.
1.Create Materialized view with data :
User needs to use WITH DATA keyword if user wants to load the data with creating materialized view.
Example :
Create materialized view MV_Customer
As
Select * from Customer WITH DATA;
2.Create Materialized view without data :
If you want to create structure of Materialized view without data no need to use WITH DATA keyword. User can use WITH NO DATA keyword in that case.
Example :
Create materialized view MV_Customer
As
Select * from Customer WITH NO DATA;
These are two types of materialized view. Materialized view is nothing but table like structure so the everybody has question in mind that how to update the data in materialized views? To update the data in materialized views user needs to refresh the data. The following syntax is used for refreshing the data in materialized view.
Refresh Materialized View :
To refresh data in materialized view user needs to use REFRESH MATERIALIZED VIEW statement.
Syntax :
REFRESH MATERIALIZED VIEW View_Name;
When you are refreshing Materialized view the MV will be locked and user will not able to fire the queries at the same time. The table will be locked.
In real life scenarios this is the big risk. So user needs to work with CONCURRENTLY keyword to refresh the view. But this reduces the speed of operations during this.
Note : Concurrently option is available only in PosgreSQL 9.4 and above versions.
REFRESH MATERIALIZED VIEW CONCURRENTLY View_Name;
The above statement will refresh the materialized view concurrently. There is on prerequisite while using CONCURRENTLY statement. The prerequisite is materialized view must have a unique index.
Drop Materialized view :
Removing or dropping materialized view is very simple. You need to use Drop materialized view keyword to drop the view.
Drop Materialized view View_name;
Real Time Industry Example with Errors :
Scenario 1 :
We need to create a materialized view for taking up the customer data with its salary from salary table.
Create materialized view MV_Customer_Data
as
Select A.Customer_No,A.Customer_Name,B.Salary
From Customer A,Salary B
Where A.Customer_No=B.Customer_No
WITH NO DATA;
If you are using WITH NO DATA keyword it will be very difficult to fetch data.
Select * from MV_Customer_Data;
The above statement will give error.
Error Code :
ERROR : Materialized view “MV_Customer_Data” has not been populated.
Hint : Use the REFRESH MATERIAZED VIEW command.
PostgreSQL is better than oracle to give you Hints of what will be the action point to execute this.
REFRESH MATERIALIZED VIEW MV_Customer_Data;
The above statement will refresh the customer data view and after that the select statement will not give you error.
Scenario 2 :
The expectation is to refresh the data concurrently in MV_Customer_Data view.
Step 1 :
Create unique index first.
Create unique index U_Customer_ID on Customer(Customer_ID);
Step 2 :
Refresh the data with using the concurrently keyword.
REFRESH MATERIALIZED VIEW CONCURRENTLY MV_Customer_Data;
This will refresh the data in materialized view concurrently. I hope you like this article on PostgreSQL Materialized view with examples. Hoping that all concepts are cleared with this PostgreSQL Materialized view article. If you have any queries related to Postgres Materialized view kindly comment it in to comments section.