Removing a user from a group

If you want to remove a user from a group but not assign that user to another group, you have to explicitly assign him or her to the public group. This causes problems because “public” is a reserved word in SQL Server’s language. So to get around the problem, enclose the word “public” in quotes.

sp_changegroup "public", username

This is one of SQL Server’s many fudges. You have to keep reminding yourself that all users are members of the public group anyway. Using this form of the sp_changegroup procedure just cancels the user’s membership in another group.