Goal Find multiple rules with the same definition (event, condition, action) on the same table. 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 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 License
Fixing Suggestion All but one are redundant. Drop the redundant rules.
Data Source system catalog only
SQL Query
SELECT schemaname, tablename, replace(definition, rulename, 'rulename') AS rule_definition, 
string_agg(rulename, ';
' ORDER BY rulename) AS rules, Count(*) AS number_of_rules FROM pg_rules GROUP BY schemaname, tablename, rule_definition HAVING Count(*)>1 ORDER BY schemaname, tablename, Count(*) DESC;

SQL statements that help generate fixes for the identified problem.

SQL Query to Generate FixDescription
WITH duplicate_rules AS (
SELECT schemaname, tablename, array_agg(rulename) AS rules_array
FROM pg_rules
GROUP BY schemaname, tablename,  replace(definition, rulename, 'rulename')
HAVING Count(*)>1)
SELECT format('DROP RULE %1$I ON TABLE %2$I.%3$I;', unnest(rules_array),  schemaname, tablename) AS statements
FROM duplicate_rules 
ORDER BY schemaname, tablename, unnest(rules_array);
Drop the rule. One of the rules must stay in place.
Collections

This query belongs to the following collections:

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:

NameDescription
Duplication of implementation elementsQueries of this catergory provide information about the duplication of the database objects.
Triggers and rulesQueries of this category provide information about triggers and rules in a database.

Further reading and related materials:

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)