how to ceck the serice in database

Question

hello ,
i have some proble in my website project
i have one serice like

in my website i select range 2222-8000

now alow to(to-100 from-900) to one user

now i add another user and give another serise like To-800 FROM 2000

but the user one already hia 900 then we can not assign to start 800 so we can asign after 900 so

how to check the number where we alow to add new user in sql check or do in c# code
help me