Grant SELECT on all tables in Redshift
You need the USAGE privilege (at least) for the schema as well:

GRANT USAGE ON SCHEMA something TO GROUP data_viewers;


Related Postgres example:


Permission for sequence in another schema


Remember you only granted permissions to already existing tables. Does not apply to tables created later. To cover those, too:

ALTER DEFAULT PRIVILEGES FOR USER role_that_creates_tables
IN SCHEMA public
GRANT SELECT ON TABLES TO GROUP data_viewers;


Amazon Redshift implemented DEFAULT PRIVILEGES as well.

Here is a complete cookbook for Postgres:


How to manage DEFAULT PRIVILEGES for USERs on a DATABASE vs SCHEMA?


Be aware of some differences between mainline Postgres and Redshift! Redshift sticks to separate users and groups, while Postgres replaced that with the universal concept of roles:


Why did PostgreSQL merge users and groups into roles?


And I am not sure how Redshift handles sequences ...