Hi,
you can use something like

group_id IN (1) AND group_id NOT IN (2)

Thats what I thought, but not working.

Interestingly, if I put

group_id IN (1) AND group_id IN (2)

the user of both groups does not show either, but

group_id IN (1)

and

group_id IN (2)

both work

Hi,
you have right, we need a SQL Where a bit more complex to make this, you can use something like:

user_id IN (SELECT user_id FROM #__user_usergroup_map WHERE group_id IN (1,2) GROUP BY user_id HAVING count(user_id)=1) AND group_id IN (1)

We need something like this because there is a INNER JOIN between Joomla User Table and Joomla Usergroups Table.

thank you that did it