利用强大的GOOGLE和几个很有用的关键字"sqlserver 恢复 用户 public"一下子就找到了,转到这里记录一下.
use testdb
declare @uname sysname
declare @asid varbinary(85)
select @uname = [Name],@asid = sid from sysusers where [name] = 'dbadmin'
use master
exec sp_addlogin @loginame = @uname,@sid = @asid