I have a Jira system that we need to do some user cleanup for. I'm blanking out on how to write this particular query. The table in question looks like this, where CHILD_ID is a username and PARENT_ID is a group name.
CHILD_ID | PARENT_ID
select child_id from my_table where parent_id <> admins
If I understand your question right, you could simply use an in query:
SELECT CHILD_ID FROM <your_table> WHERE CHILD_ID NOT IN (SELECT CHILD_ID FROM <your_table> WHERE PARENT_ID = 'admins');