Deterministic (immutable) functions that do not have input parameters

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Goal Find deterministic functions that do not have any input parameters. Make sure that it is correct because in general a deterministic function must calculate a value based on input.
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 excludes extension routines.
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 Change the function and add one or more parameters. To do so the function must be firstly dropped.
Data Source INFORMATION_SCHEMA+system catalog
SQL Query 
SELECT 
  pg_namespace.nspname AS routine_schema, 
  pg_proc.proname AS routine_name, 
 regexp_replace(pg_get_functiondef(pg_proc.oid),'[\r\n]','
','g')  AS routine_src,
 pg_type.typname AS return_type
FROM pg_catalog.pg_proc INNER JOIN pg_catalog.pg_namespace ON pg_proc.pronamespace = pg_namespace.oid
INNER JOIN pg_catalog.pg_type ON pg_proc.prorettype = pg_type.oid
WHERE pg_proc.provolatile='i'
AND pg_proc.prokind='f' 
AND pg_get_function_identity_arguments(pg_proc.oid)=''
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)
ORDER BY routine_schema, routine_name;

SQL statements that help generate fixes for the identified problem.

SQL Query to Generate FixDescription
SELECT format('DROP FUNCTION %1$I.%2$I();', pg_namespace.nspname, pg_proc.proname) AS statements
FROM pg_catalog.pg_proc INNER JOIN pg_catalog.pg_namespace ON pg_proc.pronamespace = pg_namespace.oid
WHERE pg_proc.provolatile='i'
AND pg_proc.prokind='f' 
AND pg_get_function_identity_arguments(pg_proc.oid)=''
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 pg_namespace.nspname, pg_proc.proname;
Drop the function.
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
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