use tempdb;
go

create table dbo.t (id int identity primary key, s varbinary(max), tag1 as checksum(s), tag2 as datalength(s));
create index IX_t__tag1__tag2 on dbo.t (tag1, tag2);
go

create trigger dbo.tr_t__check_uniqueness
on dbo.t
after insert, update
as
begin
 set nocount on;

 if not exists(select 1 from inserted)
  return;
 
 if exists(select 1 from inserted i join dbo.t t on t.tag1 = i.tag1 and t.tag2 = i.tag2 where i.id <> t.id and i.s = t.s)
  begin
   raiserror('Нарушена уникальность столбца s', 16, 2);
   rollback;
   return;
  end;
end;
go

if object_id('tempdb..#s', 'U') is not null
 drop table #s;

declare
 @s1 varbinary(max) = cast(replicate(cast(0x01 as varbinary(max)), 9000) as varbinary(max)),
 @s2 binary(8000) = cast(replicate(0x01, 8000) as binary(8000)),
 @s3 binary(8000) = cast(replicate(0x02, 8000) as binary(8000));

declare
 @s4 varbinary(max) = convert(varbinary(max), convert(varchar(max), @s2, 2) + convert(varchar(max), @s2, 2), 2),
 @s5 varbinary(max) = convert(varbinary(max), convert(varchar(max), @s2, 2) + convert(varchar(max), @s3, 2), 2);

select s into #s from (values (@s1), (@s2), (@s3), (@s4), (@s5)) a(s);
go

insert into dbo.t (s) select s from #s;
go

insert into dbo.t (s) select top (1) s from #s;
go

select * from dbo.t;
go

drop table dbo.t;
go