Welcome Center    Group 1
Members Questions Group 2
Admin Ops         Group 3

User 1      Group 1
User 2      Group 2
User 3      Group 3

1     Register User
2     Member
3     Admin

"SELECT * FROM topic WHERE group = 1"

"SELECT * FROM topic WHERE group = 1 AND group = 2"

"SELECT * FROM topic WHERE group = 1 AND group = 2 AND group = 3"