Goal Find named input parameters that are not referenced in the routine body. All the parameters that are presented in the routine signature declaration must be used in its body. Otherwise these are dead code elements.
Notes Refers to the column pg_proc.prokind and thus works starting from PostgreSQL 11. 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. The query does not consider the routines that are a part of an extension.
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 License
Fixing Suggestion Refer the parameter in the body or remove it from the routine signature. In case of the former, one has to use use CREATE OR REPLACE statement. In case of the latter, one has to drop the routine and create it with a new set of parameters.
Data Source INFORMATION_SCHEMA+system catalog
SQL Query
WITH routine AS (SELECT 
  pg_namespace.nspname AS routine_schema, 
  pg_proc.proname AS routine_name, 
 pg_proc.proname || '_' || pg_proc.oid AS routine_specific_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((CASE WHEN pg_proc.prosqlbody IS NULL THEN pg_proc.prosrc ELSE pg_get_function_sqlbody(pg_proc.oid) END),'[\r\n]','
','g') AS routine_body, unnest(pg_proc.proargnames) AS routine_param 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_proc.proargnames IS NOT NULL 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) AND NOT EXISTS (SELECT 1 FROM pg_catalog.pg_depend d WHERE EXISTS (SELECT 1 FROM pg_catalog.pg_extension e WHERE d.refobjid=e.oid) AND d.objid=pg_proc.oid)) SELECT routine_schema, routine_name, parameters, routine_type, routine_body, routine_param AS unused_parameter FROM routine AS r WHERE EXISTS (SELECT * FROM INFORMATION_SCHEMA.parameters AS p WHERE r.routine_schema=p.specific_schema AND r.routine_specific_name=p.specific_name AND r.routine_param=p.parameter_name AND p.parameter_mode='IN') AND routine_body NOT ILIKE '%'|| routine_param || '%' ORDER BY routine_schema, routine_name, parameters, unused_parameter;
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
Comfortability of database evolutionQueries of this category provide information about the means that influence database evolution.
Does not work in some earlier PostgreSQL versionQueries of this category provide information that was not available in some earlier PostgreSQL version
Unused implementation elementsQueries of this catergory provide information about the database objects that are not used.
User-defined routinesQueries of this category provide information about the user-defined routines

Further reading and related materials:

Reference
https://en.wikipedia.org/wiki/Dead_code
The corresponding code smells in case of cleaning code are "F4: Dead Function" and "G9: Dead Code". (Robert C. Martin, Clean Code)