Goal Find views with exactly the same subquery. There should not be multiple views with exactly the same subquery. Do remember that the same task can be solved in SQL usually in multiple different ways. Thus, the exact copies are not the only possible duplication.
Notes In the returned subquery of view the query replaces each newline character with the line break (br) tag for the better readability in case the query result is displayed in a web browser. In case of the string_agg function, the line break (br) tag is used as a part of the separator for the better readability in case the query result is displayed in a web browser.
Type Problem detection Each row in the result could represent a flaw in the design
Reliability High Few or no false-positive results
License MIT (opens in new tab)
Fixing Suggestion All but one are redundant. Drop the redundant views.
Data Source INFORMATION_SCHEMA only
SQL Query 
SELECT regexp_replace(view_definition,'[\r\n]','<br>','g') AS view_definition, views, number_of_views
FROM (SELECT  view_definition, string_agg(table_schema || '.'|| table_name,';<br>' ORDER BY table_schema || '.'|| table_name) AS views, Count(*) AS number_of_views
FROM  information_schema.views
WHERE table_schema NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)
GROUP BY view_definition
HAVING Count(*)>1) AS duplicate_views
ORDER BY number_of_views DESC;

SQL statements that help generate fixes for the identified problem.

Fix Action #1
WITH duplicate_views AS (SELECT  view_definition,  array_agg(table_schema || '.' || table_name) AS view_array
FROM  information_schema.views
WHERE table_schema NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)
GROUP BY view_definition
HAVING Count(*)>1)
SELECT format('DROP VIEW %1$s;', unnest(view_array)) AS statements
FROM duplicate_views
ORDER BY view_definition;

Drop the view. One of the views must stay in place.

SQL Query to Generate FixDescription
WITH duplicate_views AS (SELECT  view_definition,  array_agg(table_schema || '.' || table_name) AS view_array
FROM  information_schema.views
WHERE table_schema NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)
GROUP BY view_definition
HAVING Count(*)>1)
SELECT format('DROP VIEW %1$s;', unnest(view_array)) AS statements
FROM duplicate_views
ORDER BY view_definition;
Drop the view. One of the views must stay in place.

Collections

This query belongs to the following collections:

Find problems automatically

Queries, that results point to problems in the database. Each query in the collection produces an initial assessment. However, a human reviewer has the final say as to whether there is a problem or not .

NameDescription
Find problems automaticallyQueries, that results point to problems in the database. Each query in the collection produces an initial assessment. However, a human reviewer has the final say as to whether there is a problem or not .

Categories

This query is classified under the following categories:

Comfortability of database evolution

Queries of this category provide information about the means that influence database evolution.

Derived tables

Queries of this category provide information about the derived tables (views, materialized views), which are used to implement virtual data layer.

Duplication of implementation elements

Queries of this catergory provide information about the duplication of the database objects.

NameDescription
Comfortability of database evolutionQueries of this category provide information about the means that influence database evolution.
Derived tablesQueries of this category provide information about the derived tables (views, materialized views), which are used to implement virtual data layer.
Duplication of implementation elementsQueries of this catergory provide information about the duplication of the database objects.

Further reading and related materials:

https://refactoring.guru/smells/alternative-classes-with-different-interfaces
https://refactoring.guru/smells/duplicate-code
The corresponding code smell in case of cleaning code is "G5: Duplication". (Robert C. Martin, Clean Code)
Reference
https://refactoring.guru/smells/alternative-classes-with-different-interfaces
https://refactoring.guru/smells/duplicate-code
The corresponding code smell in case of cleaning code is "G5: Duplication". (Robert C. Martin, Clean Code)