42P07ERRORTier 1 — Safe✅ HIGH confidence

relation already exists

Category: Duplicate TableVersions: All Postgres versions

What this means

A CREATE TABLE, CREATE VIEW, CREATE MATERIALIZED VIEW, CREATE INDEX, or CREATE SEQUENCE statement attempted to create a relation with a name that already exists in the current schema.

Why it happens

1Running CREATE TABLE without IF NOT EXISTS in a migration that has already been applied
2A table with the same name exists in the schema the statement resolves to
3CREATE INDEX with a name that is already used by another index on any table in the schema

How to reproduce

CREATE TABLE is executed twice for the same table name.

trigger — this will ERROR

CREATE TABLE events (id SERIAL PRIMARY KEY, name TEXT);
CREATE TABLE events (id SERIAL PRIMARY KEY, name TEXT); -- triggers 42P07

ERROR: relation "events" already exists

Fix 1: Use IF NOT EXISTS

In idempotent migration scripts.

fix

CREATE TABLE IF NOT EXISTS events (
  id   SERIAL PRIMARY KEY,
  name TEXT NOT NULL
);

CREATE INDEX IF NOT EXISTS idx_events_name ON events (name);

Why this works

IF NOT EXISTS checks pg_class for a relation with the given name in the target schema. If found, the statement is suppressed with a NOTICE. The check and the creation are not atomic (a race is possible in concurrent DDL), but this is acceptable for migrations run under a migration lock.

What not to do

✗

Use DROP TABLE IF EXISTS before CREATE TABLE in migrations

Why it's wrong: Drops all data and dependent objects silently; idempotent CREATE with IF NOT EXISTS is always safer.

Sources

📚 Official docs: https://www.postgresql.org/docs/current/errcodes-appendix.html

📚 Feature docs: https://www.postgresql.org/docs/current/sql-createtable.html

Confidence assessment

✅ HIGH confidence

Well-documented and stable. IF NOT EXISTS for CREATE TABLE was added in Postgres 9.1. Edge case: index names are global within a schema, not scoped to a table; two tables cannot share an index name.