42883: undefined_function

What does it mean?

The function (or operator) called in the query was not found with this name and these argument types. PostgreSQL resolves functions by both name and argument types; if the signature does not match, this error is raised.

Why does it happen?

A misspelled function name; argument types that do not match the defined signature (e.g. a number instead of text); a missing explicit cast; the function's schema not being in search_path; the required extension not being installed.

How to fix it

Verify that the function exists and check its signature: \df function_name. Cast the arguments explicitly: SELECT fn(value::text). Add the schema prefix or set search_path. If an extension is required, install it: CREATE EXTENSION extension_name; For operator errors, make the types on both sides match.