postgres create user only if not exists [duplicate] - sql

Question

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Create PostgreSQL ROLE (user) if it doesn't exist
(12 answers)
Closed 1 year ago.
I have few CREATE user as part of myquery.sql files and it contains few other queries as well
my file looks like this
CREATE USER myuser NOLOGIN;
GRANT CONNECT on DATABSE myDataBase to myuser;
GRANT USAGE ON SCHEAMA myschema to myuser;
I have few queries like this in the same file, due to some reason I need to add new queries to same file, when execute the same file again I stuck with error user already exists, and does not reach to newly added query.
also I checked there is no IF NOT EXISTS kind of help for CREATE USER in postgres.
so how to add the check to create a USER only if not EXISTS.

Answer 1

I don't know what you mean by "there is no IF NOT EXISTS kind of help for CREATE USER in postgres". A quick search yielded this, which will let you use plpgsql to do the check:
DO
$do$
BEGIN
IF NOT EXISTS ( SELECT FROM pg_roles
WHERE rolname = 'my_user') THEN
CREATE USER myuser NOLOGIN;
GRANT CONNECT on DATABSE myDataBase to myuser;
GRANT USAGE ON SCHEMA myschema to myuser;
END IF;
END
$do$;
From here. Optionally, you can catch any exceptions of duplicate users so the remainder of your query runs smoothly, without any race conditions; there are even some bash alternatives even further down that thread.
NB: You may need to use escape character for $ (like $) if you use
the code block in a shell scripting.