Grant privileges for a particular database in PostgreSQL

Question

I'm moving from MySQL to PostgreSQL and have hit a wall with user privileges. I am used to assigning a user all privileges to all tables of a database with the following command:

# MySQL
grant all privileges on mydatabase.* to 'myuser'@'localhost' identified by 'mypassword';

It appears to me that the PostgreSQL 9.x solution involves assigning privileges to a "schema", but the effort required of me to figure out exactly what SQL to issue is proving excessive. I know that a few more hours of research will yield an answer, but I think everyone moving from MySQL to PostgreSQL could benefit from having at least one page on the web that provides a simple and complete recipe. This is the only command I have ever needed to issue for users. I'd rather not have to issue a command for every new table.

I don't know what scenarios have to be handled differently in PostgreSQL, so I'll list some of the scenarios that I have typically had to handle in the past. Assume that we only mean to modify privileges to a single database that has already been created.

(1a) Not all of the tables have been created yet, or (1b) the tables have already been created.

(2a) The user has not yet been created, or (2b) the user has already been created.

(3a) Privileges have not yet been assigned to the user, or (3b) privileges were previously assigned to the user.

(4a) The user only needs to insert, update, select, and delete rows, or (4b) the user also needs to be able to create and delete tables.

I have seen answers that grant all privileges to all databases, but that's not what I want here. Please, I am looking for a simple recipe, although I wouldn't mind an explanation as well.

I don't want to grant rights to all users and all databases, as seems to be the conventional shortcut, because that approach compromises all databases when any one user is compromised. I host multiple database clients and assign each client a different login.

It looks like I also need the USAGE privilege to get the increasing values of a serial column, but I have to grant it on some sort of sequence. My problem got more complex.

Answer 1

Basic concept in Postgres

Roles are global objects that can access all databases in a db cluster - given the required privileges.

A cluster holds many databases, which hold many schemas. Schemas (even with the same name) in different DBs are unrelated. Granting privileges for a schema only applies to this particular schema in the current DB (the current DB at the time of granting).

Every database starts with a schema public by default. That's a convention, and many settings start with it. Other than that, the schema public is just a schema like any other.

Coming from MySQL, you may want to start with a single schema public, effectively ignoring the schema layer completely. I am using dozens of schema per database regularly.
Schemas are a bit (but not completely) like directories in the file system.

Once you make use of multiple schemas, be sure to understand search_path setting:

• How does the search_path influence identifier resolution and the "current schema"

Default privileges

Per documentation on GRANT:

PostgreSQL grants default privileges on some types of objects to PUBLIC. No privileges are granted to PUBLIC by default on tables, columns, schemas or tablespaces. For other types, the default privileges granted to PUBLIC are as follows: CONNECT and CREATE TEMP TABLE for databases; EXECUTE privilege for functions; and USAGE privilege for languages.

All of these defaults can be changed with ALTER DEFAULT PRIVILEGES:

• Grant all on a specific schema in the db to a group role in PostgreSQL

Group role

Like @Craig commented, it's best to GRANT privileges to a group role and then make a specific user member of that role (GRANT the group role to the user role). this way it is simpler to deal out and revoke bundles of privileges needed for certain tasks.

A group role is just another role without login. Add a login to transform it into a user role. More:

• Why did PostgreSQL merge users and groups into roles?

Recipe

Say, we have a new database mydb, a group mygrp, and a user myusr ...

While connected to the database in question as superuser (postgres for instance):

REVOKE ALL ON DATABASE mydb FROM public;  -- shut out the general public
GRANT CONNECT ON DATABASE mydb TO mygrp;  -- since we revoked from public

GRANT USAGE ON SCHEMA public TO mygrp;

To assign a user all privileges to all tables like you wrote (I might be more restrictive):

GRANT ALL ON ALL TABLES IN SCHEMA public TO mygrp;
GRANT ALL ON ALL SEQUENCES IN SCHEMA public TO mygrp; -- don't forget those

To set default privileges for future objects, run for every role that creates objects in this schema:

ALTER DEFAULT PRIVILEGES FOR ROLE myusr IN SCHEMA public
GRANT ALL ON TABLES TO mygrp;

ALTER DEFAULT PRIVILEGES FOR ROLE myusr IN SCHEMA public
GRANT ALL ON SEQUENCES TO mygrp;

-- more roles?

Now, grant the group to the user:

GRANT mygrp TO myusr;

Related answer:

• PostgreSQL - DB user should only be allowed to call functions

Alternative (non-standard) setting

Coming from MySQL, and since you want to keep privileges on databases separated, you might like this non-standard setting db_user_namespace. Per documentation:

This parameter enables per-database user names. It is off by default.

Read the manual carefully. I don't use this setting. It does not void the above.