use tempdb;
set ansi_nulls, quoted_identifier, xact_abort on;
go

create table dbo.t1 (id int primary key);
create table dbo.t2 (id int primary key);

insert into dbo.t1
 (id)
output
 inserted.id into dbo.t2 (id)
 select top (1000000)
  row_number() over (order by 1/0)
 from
  master.dbo.spt_values a cross join
  master.dbo.spt_values b;
go

declare @c int;

set statistics xml, io, time on;
select @c = count(*) from dbo.t1 a where not exists(select 1 from dbo.t2 where id = a.id) option (maxdop 1, loop join);
select @c = count(*) from dbo.t1 a where not exists(select 1 from dbo.t2 where id = a.id) option (maxdop 1, merge join);
set statistics xml, io, time off;
go

drop table dbo.t1, dbo.t2;
go

Table 't2'. Scan count 0, logical reads 3062509, physical reads 0, page server reads 0, read-ahead reads 14, page server read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob page server reads 0, lob read-ahead reads 0, lob page server read-ahead reads 0.
Table 't1'. Scan count 1, logical reads 1615, physical reads 0, page server reads 0, read-ahead reads 0, page server read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob page server reads 0, lob read-ahead reads 0, lob page server read-ahead reads 0.

(1 row affected)

 SQL Server Execution Times:
   CPU time = 1266 ms,  elapsed time = 1290 ms.
Table 't2'. Scan count 1, logical reads 1615, physical reads 0, page server reads 0, read-ahead reads 0, page server read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob page server reads 0, lob read-ahead reads 0, lob page server read-ahead reads 0.
Table 't1'. Scan count 1, logical reads 1615, physical reads 0, page server reads 0, read-ahead reads 0, page server read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob page server reads 0, lob read-ahead reads 0, lob page server read-ahead reads 0.

(1 row affected)

 SQL Server Execution Times:
   CPU time = 250 ms,  elapsed time = 300 ms.