Goal This query identifies superfluous function calls within routines and views, specifically targeting invocations of coalesce(), concat(), or concat_ws() that are supplied with only a single argument. These functions are variadic and designed to operate on multiple values (e.g., returning the first non-null value or joining strings). When called with a single argument, they function as an identity operation, returning the input unchanged. This pattern indicates either a coding error (missing arguments) or redundant logic that should be removed to simplify the expression.
Notes Refers to the column pg_proc.prokind and thus works starting from PostgreSQL 11. The query uses system information function pg_get_viewdef to get the view subquery pretty printed, i.e., without excessive brackets. The query does not consider the routines that are a part of an extension. In the returned body of subquery of view/materialized view/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. If the arguments of the invocation have brackets, then the query returns false positive results.
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 Add additional arguments to the invocation or remove the invocation.
Data Source INFORMATION_SCHEMA+system catalog
SQL Query
WITH objects AS (
    -- 1. Views and Materialized Views
    SELECT 
        n.nspname AS schema_name, 
        c.relname AS object_name, 
        CASE WHEN c.relkind='v' THEN 'VIEW' WHEN c.relkind='m' THEN 'MATERIALIZED VIEW' END AS object_type,
        pg_get_viewdef(c.oid, true) AS object_definition
    FROM pg_namespace AS n 
    INNER JOIN pg_authid AS a ON n.nspowner=a.oid
    INNER JOIN pg_class AS c ON n.oid=c.relnamespace
    WHERE (n.nspname='public' OR a.rolname<>'postgres')
    AND c.relkind IN ('v','m')

    UNION ALL

    -- 2. Functions and Procedures
    SELECT 
        pg_namespace.nspname AS schema_name, 
        pg_proc.proname || '(' || pg_get_function_identity_arguments(pg_proc.oid) || ')' AS object_name,
        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 object_type,
        pg_get_functiondef(pg_proc.oid) AS object_definition
    FROM pg_catalog.pg_proc
    JOIN pg_catalog.pg_namespace ON pg_proc.pronamespace = pg_namespace.oid
    WHERE 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_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)
),
cleaned_objects AS (
    SELECT 
        schema_name,
        object_name,
        object_type,
        object_definition,
        -- Clean the definition by removing strings and quoted identifiers.
        -- This is crucial so that commas inside strings (e.g., "Lastname, Firstname") 
        -- are not misinterpreted as argument separators.
        -- 1. Replace 'text' -> $STR$
        -- 2. Replace "text" -> $ID$
        regexp_replace(
            regexp_replace(object_definition, '''([^'']|'''')*''', '$STR$', 'g'), 
            '"([^"]|"")*"', '$ID$', 'g'
        ) AS clean_def
    FROM objects
)
SELECT 
    schema_name, 
    object_name, 
    object_type, 
    regexp_replace(object_definition,'[\r\n]','
','g') AS object_def FROM cleaned_objects WHERE -- Regular expression to find single-argument calls: -- \y(coalesce|concat|concat_ws) : Function name (with word boundary) -- \s*\( : Opening parenthesis -- (?: : Content group -- [^(),] : 1. Any character that is not a comma or parenthesis -- | : OR -- \((?:[^()]|\([^()]*\))*\) : 2. Nested parentheses (handles logic like string_agg(a,b) inside the argument) -- )* : Repeat content -- \) : Closing parenthesis -- If this pattern matches, it means there are no top-level commas (outside nested parentheses), implying only one argument. clean_def ~* '\y(coalesce|concat|concat_ws)\s*\((?:[^(),]|\((?:[^()]|\([^()]*\))*\))*\)' ORDER BY schema_name, object_type, object_name;
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
Derived tablesQueries of this category provide information about the derived tables (views, materialized views), which are used to implement virtual data layer.
Does not work in some earlier PostgreSQL versionQueries of this category provide information that was not available in some earlier PostgreSQL version
System-defined functionsQueries of this category provide information about the use of system-defined functions.
User-defined routinesQueries of this category provide information about the user-defined routines

Further reading and related materials:

Reference
http://www.postgresqltutorial.com/postgresql-coalesce/