ALTER GROUP -- Add users to a group, remove users from a group
ALTER GROUP name ADD USER username [, ... ]
ALTER GROUP name DROP USER username [, ... ]
ALTER GROUP is used to add or remove users from a group. Only database superusers can use this command. Adding a user to a group does not create the user. Similarly, removing a user from a group does not drop the user itself.
Use CREATE GROUP to create a new group and DROP GROUP to remove a group.
Add users to a group:
ALTER GROUP staff ADD USER karl, john
Remove a user from a group:
ALTER GROUP workers DROP USER beth
There is no ALTER GROUP statement in SQL92. The concept of roles is similar.