undefined_object extension “…” does not exist — 42704

Symptoms

A statement referenced an extension that is not installed in the current database. PostgreSQL raises SQLSTATE 42704 (undefined_object).

• The named extension isn’t installed here.
• Common in ALTER EXTENSION/DROP EXTENSION.
• Extensions are per-database.

What the server log shows

ERROR:  extension "pg_trgm" does not exist

Why PostgreSQL raises this — what the manual says

the DROP EXTENSION reference (Description):

“DROP EXTENSION removes extensions from the database.”

Extensions are installed per database via CREATE EXTENSION. Referencing one that was never installed (or installed in a different database) cannot be resolved, so PostgreSQL reports 42704.

Common causes

• The extension was never installed in this database.
• A typo in the extension name.
• Connected to the wrong database.

How to fix it

1. Install it: CREATE EXTENSION pg_trgm; (if the contrib package is present).
2. List installed extensions: \dx or query pg_extension.
3. Use DROP EXTENSION IF EXISTS for idempotency; verify the database.

Related & next steps

• SQLSTATE 42704 — Undefined Object (full reference)
• Message: language does not exist
• Glossary: Extension

Reference: PostgreSQL 18 — DROP EXTENSION.