Goal Find routines that contain a statement that sorts rows based on random values. This can be used to find a random subset of rows. It is a computationally expensive operation.
Notes Refers to the column pg_proc.prokind and thus works starting from PostgreSQL 11. There could be multiple routines with the same name but with different parameters in the same schema (overloading). Thus, for the unique identification of the routine it is necessary to present also its parameters in addition to the schema name and routine name. In the returned body of routine 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.
Type Problem detection Each row in the result could represent a flaw in the design
Reliability Medium Medium number of false-positive results
License MIT (opens in new tab)
Fixing Suggestion Bill Karwin in his book of SQL database design antipatterns offers various alternatives for finding a random subset of rows.
Data Source INFORMATION_SCHEMA+system catalog
SQL Query 
SELECT 
  pg_namespace.nspname AS routine_schema, 
  pg_proc.proname AS routine_name, 
  pg_get_function_identity_arguments(pg_proc.oid) AS parameters,
  CASE WHEN pg_proc.prokind='f' THEN 'FUNCTION'
  WHEN pg_proc.prokind='p' THEN 'PROCEDURE'
  WHEN pg_proc.prokind='w' THEN 'WINDOW FUNCTION' END AS routine_type,
 regexp_replace(pg_get_functiondef(pg_proc.oid),'[\r\n]','<br>','g')  AS routine_src
FROM 
  pg_catalog.pg_proc, 
  pg_catalog.pg_namespace
WHERE 
  pg_proc.pronamespace = pg_namespace.oid 
  AND pg_proc.prokind<>'a'
  AND pg_proc.proname NOT IN ('f_assume_you_must_use_files', 'f_check_format_comma_separated_list', 'f_check_password', 'f_default_value_with_no_match') AND 
 pg_get_functiondef(pg_proc.oid)~*'order[[:space:]]+by[[:space:]]+random[(][)]'
AND pg_namespace.nspname NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)
ORDER BY routine_schema, routine_name;

Categories

This query is classified under the following categories:

Does not work in some earlier PostgreSQL version

Queries of this category provide information that was not available in some earlier PostgreSQL version

Performance

Queries of this category provide information about indexes in a database.

User-defined routines

Queries of this category provide information about the user-defined routines

NameDescription
Does not work in some earlier PostgreSQL versionQueries of this category provide information that was not available in some earlier PostgreSQL version
PerformanceQueries of this category provide information about indexes in a database.
User-defined routinesQueries of this category provide information about the user-defined routines

Further reading and related materials:

This is one of the antipatterns from the Bill Karwin's book of SQL antipatterns. See Chapter 16: Random Selection.
Reference
This is one of the antipatterns from the Bill Karwin's book of SQL antipatterns. See Chapter 16: Random Selection.