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

You can do it in your batch file by parsing the output of:

SELECT * FROM pg_user WHERE usename = 'my_user'

and then running psql.exe once again if the role does not exist.