What is role?

When several users need to perform the similar actions in a particular database (no corresponding Windows User Group in this case), they will be able to add a database role. The database role can specify the group of database users which they can access the same database objects.

To create a role by using the SQL command:
CREATE ROLE name;

The members of database roles can be divided into the following categories:
Windows user group or user accounts; SQL Server Login; Other roles

SQL Server's Security architecture includes several specific roles with implied authority. In addition, to the database, the role is created by the owner. There are two kinds of pre-defined roles.

The roles created by these members can be divided into the following categories:
Fixed server role; Fixed database role; User Defined

In order to bootstrap the database system, a freshly initialized system always contains one predefined role. This role is always a "superuser”, and by default (unless altered when running initdb ) it will have the same name as the operating system user that initialized the database cluster. Customarily, this role will be named postgres. In order to create more roles you first have to connect as this initial role. Every connection to the database server is made in the name of some particular role, and this role determines the initial access privileges for commands issued on that connection. The role name to use for a particular database connection is indicated by the client that is initiating the connection request in an application-specific fashion. Many applications assume the name of the current operating system user by default (including create user and psql ). Therefore it is often convenient to maintain a naming correspondence between roles and operating system users.

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