PostgreSQL – DROP VIEWS Statement

A view in PostgreSQL can be seen as a virtual table that can contain all rows of a table or selected rows from one or more tables. Views allow us to see limited data instead of the complete information stored in a table. A view can be created from one or many base tables (the table from which the view is created). Various operations can be performed on views, such as creating, updating, and deleting views. Here, we will primarily focus on dropping or deleting views.

What is a View?

A view is a virtual table that provides a way to present data from one or more tables in a specific format. It can include all rows from a table or a subset of rows with specific columns. Views help in simplifying complex queries, enhancing security by restricting access to specific data, and maintaining data consistency.

To understand the DROP VIEW statement, we’ll take a sample table named “Students” as shown here:

CREATE TABLE Students (
    admit_id SERIAL PRIMARY KEY,
    stu_name VARCHAR(255) NOT NULL,
    branch VARCHAR(255) NOT NULL,
    marks INTEGER
);

INSERT INTO Students (stu_name, branch) VALUES
('101', 'Ravi', 'Science', '95'),
('102', 'Rohan', 'Science', '90'),
('103', 'Rajesh', 'Commerce', '95'),
('104', 'Ritika', 'Commerce', '92')
('105', 'Sagar', 'Arts', '99')
('106', 'Sahil', 'Arts', '90')
('107', 'Sakshi', 'Science', '95');

Students table

PostgreSQL DROP VIEW Statement

As the name suggests, The DROP VIEW statement removes a view from the database.

Syntax:

The basic DROP VIEW syntax is as follows:

DROP VIEW [IF EXISTS] view_name
[CASCADE | RESTRICT]

Parameters:

Now let us understand the meaning of the keywords used in the above syntax one by one:

1. DROP VIEW: Keywords used to specify the name of the view that needs to be dropped.
2. IF EXISTS: Ensures that the view is dropped only if it exists. If the view does not exist, no error is thrown.
3. view_name: The name of the view to be dropped.
4. RESTRICT: Does not allow the view to be deleted if any other objects depend on it. This is the default option.
5. CASCADE: Automatically drops objects that depend on the view and all objects that depend on those objects.

Dropping Multiple Views

It is also possible to delete multiple views using the single DROP VIEW  statement using the following syntax:

DROP VIEW [IF EXISTS] view_name1, view_name2, ...;

Creating Views

Now to understand the DROP VIEW statement, we need to first create a view that we can drop/delete later. Below is the statement that creates a view named “StudentsView” based on the information stored in the table “Students“.

CREATE OR REPLACE VIEW StudentsView
AS 
SELECT 
   admit_id,
   stu_name,
   branch 
FROM
Students
WHERE branch ='Science';

Output :  

StudentsView

So we have successfully created a view that contains three columns (‘admit_id’, ‘stu_name’, ‘branch’)from the original table. Let us create one more view named “myview” that is based on the ‘StudentsView’ using the following statement:

CREATE OR REPLACE VIEW myview 
AS 
SELECT 
   admit_id,
   stu_name 
FROM 
StudentsView 
WHERE stu_name ='Sakshi';

Output : 

myview

Since this view has been created from the first view named “StudentsView“, hence other objects depend on “StudentsView“. Now let us try to drop the view “StudentsView” using the DROP VIEW statement as shown here:

DROP VIEW StudentsView;

Output:

ERROR:  cannot drop view studentsview because other objects depend on it
DETAIL:  view myview depends on view studentsview

HINT: Use DROP … CASCADE to drop the dependent objects too.

Since RESTRICT was the default option hence it will not allow the view to be deleted if any other objects are depending on it and hence an error has been raised here. However, if we try to drop the ‘myview’, it can be simply dropped.

DROP VIEW myview;

Output:

DROP VIEW
Query returned successfully in 73 msec.

So this how we can create and drop views in PostgreSQL. To check whether the view has been successfully dropped or not, simply run the ‘SELECT * FROM view_name’ if it still exists or has been dropped. In this case, if we run the below Query:

SELECT * FROM myview

then an error will be raised showing that myview does not exist as we have already dropped “myview“.