The PostgreSQL 42P13 error occurs when creating or altering a function with invalid syntax, missing parameters, or conflicting definitions. This prevents the database from parsing and storing the function correctly, requiring syntax fixes and validation.
The "42P13: invalid_function_definition" error in PostgreSQL indicates that the database cannot accept a function definition due to syntax errors, semantic issues, or conflicts with existing functions. PostgreSQL functions must follow strict syntax rules including proper parameter declarations, return type specifications, and language definitions. This error typically appears when using CREATE FUNCTION or ALTER FUNCTION statements with problems like: - Missing or incorrect parameter types - Invalid return type specifications - Language declaration errors - Syntax errors in the function body - Conflicts with existing function signatures PostgreSQL validates function definitions against the system catalog and SQL standards, rejecting definitions that don't meet requirements. The error prevents the function from being created or modified until all issues are resolved.
Examine your CREATE FUNCTION statement for syntax errors. Ensure all parameters have valid data types and the return type is correctly specified.
Example of correct syntax:
CREATE FUNCTION calculate_total(price numeric, quantity integer)
RETURNS numeric AS $$
BEGIN
RETURN price * quantity;
END;
$$ LANGUAGE plpgsql;Common issues to check:
- Missing parameter types: (price, quantity) instead of (price numeric, quantity integer)
- Incorrect return type: RETURNS void when function returns a value
- Missing language declaration: $$ LANGUAGE plpgsql;
Ensure the function body matches the declared language. SQL functions and PL/pgSQL functions have different syntax requirements.
For SQL functions:
CREATE FUNCTION add_numbers(a integer, b integer)
RETURNS integer AS $$
SELECT a + b;
$$ LANGUAGE sql;For PL/pgSQL functions:
CREATE FUNCTION add_numbers(a integer, b integer)
RETURNS integer AS $$
BEGIN
RETURN a + b;
END;
$$ LANGUAGE plpgsql;Mixing SQL syntax with PL/pgSQL language declaration (or vice versa) causes 42P13 errors.
PostgreSQL doesn't allow multiple functions with the same name and parameter types. Use \dF or query the pg_proc catalog to check for existing functions:
-- List functions with similar names
SELECT proname, pronargs, proargtypes::regtype[]
FROM pg_proc
WHERE proname LIKE '%your_function_name%';
-- Or use psql command
\df your_function_nameIf a conflict exists, you need to:
1. Drop the existing function: DROP FUNCTION IF EXISTS your_function_name(parameter_types);
2. Use a different function name
3. Change parameter types to create a different signature
The function body (between the $$ delimiters) must be valid SQL or PL/pgSQL. Common syntax errors include:
- Missing semicolons in PL/pgSQL blocks
- Unmatched parentheses or quotes
- Invalid variable declarations
- Incorrect control structures
Test the function body separately if possible:
-- Test the SQL part separately
SELECT price * quantity;
-- Or test PL/pgSQL logic in a DO block
DO $$
DECLARE
result numeric;
BEGIN
result := 10.99 * 3;
RAISE NOTICE 'Result: %', result;
END;
$$;PostgreSQL usually provides additional context in the error message. Look for lines like:
ERROR: 42P13: invalid_function_definition
DETAIL: SQL function "calculate_total" must return "numeric"
CONTEXT: SQL statement "CREATE FUNCTION calculate_total..."The DETAIL and CONTEXT sections often pinpoint the exact issue. Common patterns:
- "must return [type]" - return type mismatch
- "parameter [name] has pseudo-type [type]" - invalid parameter type
- "function already exists with same name and argument types" - name conflict
- "syntax error at or near [token]" - specific syntax error
While CREATE OR REPLACE FUNCTION can help with updates, it may mask underlying issues. Use it only after verifying your function is correct:
-- First, ensure your function syntax is valid
CREATE OR REPLACE FUNCTION calculate_total(price numeric, quantity integer)
RETURNS numeric AS $$
BEGIN
RETURN price * quantity;
END;
$$ LANGUAGE plpgsql;Important notes:
- OR REPLACE only works if the parameter types match exactly
- It won't fix syntax errors in the function body
- Consider using DROP FUNCTION IF EXISTS followed by CREATE FUNCTION for clearer error messages
PostgreSQL function definitions involve several validation steps:
1. Parser Validation: The SQL parser checks basic syntax before any catalog lookups.
2. Catalog Validation: PostgreSQL checks the pg_proc catalog for conflicts and validates types against pg_type.
3. Language Handler: The specified language (sql, plpgsql, etc.) must be installed and available.
4. Security Context: Functions with SECURITY DEFINER have additional permission checks.
Edge Cases:
- Functions with OUT parameters have different syntax requirements
- VARIADIC parameters must be the last parameter
- Functions returning SETOF require different syntax
- Default parameter values must be constants or immutable expressions
Debugging Tips:
- Use \set VERBOSITY verbose in psql for more detailed error messages
- Check PostgreSQL server logs for additional context
- Test function creation in a fresh database to isolate environment issues
Version Differences:
- PostgreSQL 14+ has stricter type checking for some edge cases
- Older versions may accept syntax that newer versions reject
- Extension functions (like PostGIS) may have additional requirements
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