I am creating a db that needs a very high security level. I have multiple users on the server, but I need to restrict the access to my db to only one of them. I tried setting the "Single User" option for my db, but then none of the users could access the db. I tried then deleting users, changing roles, etc. but nothing helped. Oh, this is my first serious db so I was a bit chaotic and random in my ideas, so help pleaseeee.....

grant all permissions to one of them and set for him/her username ana password
while connection to database use the username and the password for connecting