duplicate_object extension “…” already exists — 42710

Symptoms

A CREATE EXTENSION named an extension that is already installed in the database. PostgreSQL raises SQLSTATE 42710 (duplicate_object).

• The extension already exists in this database.
• Common in migration scripts run more than once.
• Use IF NOT EXISTS for idempotency.

What the server log shows

ERROR:  extension "pgcrypto" already exists

Why PostgreSQL raises this — what the manual says

the CREATE EXTENSION reference (Description):

“There must not be an extension of the same name already loaded.”

Each extension can be installed once per database (tracked in pg_extension). Re-creating one that already exists collides with the installed object, so PostgreSQL reports 42710.

Common causes

• Re-running a migration/setup script that installs the extension.
• The extension was already installed by another process.
• Template database already including the extension.

How to fix it

1. Use CREATE EXTENSION IF NOT EXISTS pgcrypto; for idempotency.
2. Check existing extensions: SELECT extname FROM pg_extension;.
3. To upgrade, use ALTER EXTENSION … UPDATE instead of re-creating.

Related & next steps

• SQLSTATE 42710 — Duplicate Object (full reference)
• Message: extension is not available
• Glossary: Extension

Reference: PostgreSQL 18 — CREATE EXTENSION.