CREATE TABLE dbo.Users (
  Id int not null identity(1,1) primary key,
  Code varchar(...),
  FirstAttribute ...,
  SecondAttribute ...,
  ...
)go
CREATE INDEX idx_Users_Code ON dbo.Users(Code)
go

CREATE TABLE dbo.Links (
  UserId1 int not null,
  UserId2 int not null,
  Weight ...,
  CONSTRAINT pk_Links PRIMARY KEY CLUSTERED (UserId1, UserId2)
)go