Goal Domains are like words that can be used to construct generalized claims about the real world (table predicates). Better not to duplicate the words in the dictionary.
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 Rename a domain. In case of duplication drop the duplicates and refactor the database so that the remaining domain will be used everywhere it is needed.
Data Source INFORMATION_SCHEMA only
SQL Query 
WITH domains AS (SELECT domain_schema, domain_name
FROM information_schema.domains
WHERE domain_schema NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL))
SELECT domain_name, string_agg(domain_schema,';<br>' ORDER BY domain_schema) AS schemas, Count(*) AS number_of_domains
FROM domains
GROUP BY domain_name
HAVING Count(*)>1
ORDER BY domain_name, Count(*) DESC;

SQL statements that help generate fixes for the identified problem.

Fix Action #1
WITH domains AS (SELECT domain_schema, domain_name
FROM information_schema.domains
WHERE domain_schema NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)),
duplicates AS (SELECT domain_name
FROM domains
GROUP BY domain_name
HAVING Count(*)>1)
SELECT format('DROP DOMAIN %1$I.%2$I;', domain_schema, domain_name) AS statements
FROM domains
WHERE domain_name IN (SELECT domain_name
FROM duplicates)
ORDER BY domain_schema, domain_name;

Drop the domain.

SQL Query to Generate FixDescription
WITH domains AS (SELECT domain_schema, domain_name
FROM information_schema.domains
WHERE domain_schema NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)),
duplicates AS (SELECT domain_name
FROM domains
GROUP BY domain_name
HAVING Count(*)>1)
SELECT format('DROP DOMAIN %1$I.%2$I;', domain_schema, domain_name) AS statements
FROM domains
WHERE domain_name IN (SELECT domain_name
FROM duplicates)
ORDER BY domain_schema, domain_name;
Drop the domain.

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.

Domains

Queries of this category provide information about reusable specifications of column properties.

Duplication of implementation elements

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

Naming

Queries of this category provide information about the style of naming.

NameDescription
Comfortability of database evolutionQueries of this category provide information about the means that influence database evolution.
DomainsQueries of this category provide information about reusable specifications of column properties.
Duplication of implementation elementsQueries of this catergory provide information about the duplication of the database objects.
NamingQueries of this category provide information about the style of naming.

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)