Create PostgreSQL ROLE (user) if it doesn't exist

Question

How do I write an SQL script to create a ROLE in PostgreSQL 9.1, but without raising an error if it already exists?

The current script simply has:

CR         


        

Answer 1

The same solution as for Simulate CREATE DATABASE IF NOT EXISTS for PostgreSQL? should work - send a CREATE USER … to \gexec.

Workaround from within psql

SELECT 'CREATE USER my_user'
WHERE NOT EXISTS (SELECT FROM pg_catalog.pg_roles WHERE rolname = 'my_user')\gexec

Workaround from the shell

echo "SELECT 'CREATE USER my_user' WHERE NOT EXISTS (SELECT FROM pg_catalog.pg_roles WHERE rolname = 'my_user')\gexec" | psql

See accepted answer there for more details.