Duplicate rules

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 (opens in new tab)
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, ';<br>' 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.

Fix Action #1

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.

SQL Query to Generate Fix Description

SQL Query to Generate Fix	Description
`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.

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:

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 .

Name	Description
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 .

Categories

This query is classified under the following categories:

Duplication of implementation elements

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

Triggers and rules

Queries of this category provide information about triggers and rules in a database.

Name	Description
Duplication of implementation elements	Queries of this catergory provide information about the duplication of the database objects.
Triggers and rules	Queries of this category provide information about triggers and rules in a database.

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)