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A routine is invoked only once

Query goal: Find user-defined routines that are invoked by exactly one user-defined routine.
Notes about the query: The query only considers routines that have SQL-standard function body. The function any_value that is used in the query was added to PostgreSQL 16. 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. 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.
Query type: Problem detection (Each row in the result could represent a flaw in the design)
Query reliability: Medium (Medium number of false-positive results)
Query license: MIT License
Fixing suggestion: If a routine is used only by one routine, then perhaps it is better to merge these.
Data source: INFORMATION_SCHEMA+system catalog
SQL query: Click on query to copy it

WITH routines AS (SELECT 
  pg_namespace.nspname AS routine_schema, 
  pg_proc.proname AS routine_name, 
  pg_proc.proname || '_' || pg_proc.oid AS 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(pg_get_functiondef(pg_proc.oid),'[\r\n]','<br>','g')  AS routine_src,
  pg_language.lanname AS routine_language
FROM 
  pg_catalog.pg_proc, 
  pg_catalog.pg_namespace,
  pg_catalog.pg_language
WHERE 
  pg_proc.pronamespace = pg_namespace.oid 
  AND pg_proc.prolang = pg_language.oid  
  AND pg_proc.prokind<>'a'  
  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)),
once_used_routines AS (SELECT routine_schema, routine_name, any_value (specific_schema || '.' || regexp_replace(specific_name,'_[0-9]+$','') || '(' || pg_get_function_identity_arguments(translate(substring(specific_name,'_[0-9]+$'),'_','')::int::oid) || ')') AS the_invoker
FROM INFORMATION_SCHEMA.routine_routine_usage
WHERE routine_schema NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)
GROUP BY routine_schema, routine_name
HAVING Count(*)=1)
SELECT r.routine_schema, r.routine_name, parameters, routine_type, routine_src, the_invoker
FROM routines AS r INNER JOIN once_used_routines AS our ON r.routine_schema=our.routine_schema AND r.specific_name=our.routine_name
ORDER BY r.routine_schema, r.routine_name, parameters;

Categories where the query belongs to

Category nameCategory description
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
User-defined routinesQueries of this category provide information about the user-defined routines

Reference materials for further reading

Reference
https://www.enterprisedb.com/blog/guide-any-value-functionality-postgresql-16

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