ServiceDesk

The user interface does not allow for the adding of multiple users in one process. You will need to add them one user at a time.

Making the addition by SQL should be possibly by adding the necessary information to the UserGroups table. 

The table that stores the User Group relationship is the UserGroup table... inserting a row into that table would look like this:

insert into UserGroup (UserGroupID, UserID, GroupID)
values (NEWID(), '<user id>', '<group id>')

To make the SQL easier (not having to manually fetch IDs) you could make the INSERT look like the following:

insert into UserGroup (UserGroupID, UserID, GroupID)
values (NEWID(),

(SELECT UserID FROM [User] WHERE PrimaryEmail = 'admin@symantec.com'),

(SELECT GroupID FROM [Group] WHERE GroupName = 'Administrators'))

This way you can specify something more meaningful, like the PrimaryEmail/GroupName