Multiple database group users for one database For a blog post, I have db design of 1 database in D7, the database contains multiple database users:  

Anonymous - Only Read privilege on Database
Writer - CRUD privilege on Database
Admin - Has all privilege to Database

How do I achieve this in Drupal 7 ? The settings.php in Drupal has only one database connection section, as I'd need to connect the database from all 3 database users, and change the database user when they log in, like when Admin logs in, he'll also be admin database user, and so on...
Although the question is a little unclear, it sounds like you just need 3 roles in your Drupal install


Administrator
Writer
Anonymous ( built-in )


You can add the roles at /admin/people/permissions/roles and configure access permissions for each role, regarding node creation etc, at /admin/people/permissions