ERROR 42P07: Relation already exists in Postgres

Error Message#

ERROR: relation "users" already exists

Description#

This error occurs when attempting to create a database object (table, view, sequence, or index) that already exists in the database.

Causes#

• Attempting to create a table that already exists
• Running migrations multiple times
• Failed rollbacks of previous migrations
• Case sensitivity confusion (PostgreSQL treats "users" and "Users" as the same by default)
• Object exists in another schema within the search path

Solutions#

1. Use IF NOT EXISTS clause#

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

2. Drop the existing relation first#

DROP TABLE IF EXISTS your_table_name;
CREATE TABLE your_table_name (
    id SERIAL PRIMARY KEY,
    name TEXT
);

3. Check if the relation exists#

-- Verify if table exists
SELECT EXISTS (
   SELECT FROM information_schema.tables
   WHERE table_schema = 'public'
   AND table_name = 'your_table_name'
);

-- Find all tables with this name across schemas
SELECT n.nspname AS schema_name, c.relname AS table_name
FROM pg_class c
JOIN pg_namespace n ON n.oid = c.relnamespace
WHERE c.relname = 'your_table_name' AND c.relkind = 'r';

4. Use schema qualification#

CREATE TABLE my_schema.your_table_name (
    id SERIAL PRIMARY KEY,
    name TEXT
);

Prevention Best Practices#

1. Always use idempotent operations with IF NOT EXISTS and IF EXISTS clauses
2. Implement proper migration patterns with version control
3. Use schema version tracking
4. Follow consistent naming conventions
5. Wrap related DDL statements in transactions