Hi, try this
declare  @a table (x int null)
insert into  @a(x) values (1)
insert into  @a(x) values (2)
insert into  @a(x) values (3)
insert into  @a(x) values (4)
insert into  @a(x) values (5)
insert into  @a(x) values (6)
insert into  @a(x) values (7)
declare  @b-2 table (x int null)
insert into  @b-2(x) values (1)
insert into  @b-2(x) values (3)
select * from  @a aa left outer join  @b-2 bb on aa.x = bb.x where bb.x is null