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

create table dbo.t1 (id int constraint PK_t1 primary key);
create table dbo.t2 (id int);

insert into dbo.t1 (id) values (1);
insert into dbo.t2 (id) values (2);

update statistics dbo.t1 with rowcount = 10000;
update statistics dbo.t2 with rowcount = 10000;

select 't1', %%lockres%%, id from dbo.t1;
select 't2', %%lockres%%, id from dbo.t2;
go

set statistics xml on;
dbcc traceon(1200, 3604, -1);
select
 t.id
from
 (
  select id from dbo.t1 with (repeatableread)
  union all
  select id from dbo.t2 with (repeatableread)
 ) t (id)
order by
 t.id
option
 (merge join);
dbcc traceoff(1200, 3604, -1);
set statistics xml off;

alter table dbo.t1 drop constraint PK_t1;
select 't1', %%lockres%%, id from dbo.t1;

print '';
print '----------------------------------------------------------------------';
print '';

set statistics xml on;
dbcc traceon(1200, 3604, -1);
select
 t.id
from
 (
  select id from dbo.t1 with (repeatableread)
  union all
  select id from dbo.t2 with (repeatableread)
 ) t (id)
order by
 t.id
option
 (merge join);
dbcc traceoff(1200, 3604, -1);
set statistics xml off;
go

drop table dbo.t1, dbo.t2;
go

Process 70 acquiring IS lock on OBJECT: 2:498816839:0  (class bit2000000 ref1) result: OK
Process 70 acquiring IS lock on OBJECT: 2:466816725:0  (class bit2000000 ref1) result: OK
Process 70 acquiring IS lock on PAGE: 2:4:224  (class bit2000000 ref0) result: OK
Process 70 acquiring S lock on RID: 2:4:224:0 (class bit2000000 ref0) result: OK
Process 70 acquiring IS lock on PAGE: 2:5:168  (class bit2000000 ref0) result: OK
Process 70 acquiring S lock on KEY: 2:4035225289354772480 (8194443284a0) (class bit2000000 ref1) result: OK
Process 70 releasing lock reference on KEY: 2:4035225289354772480 (8194443284a0)

Process 70 acquiring IS lock on OBJECT: 2:498816839:0  (class bit2000000 ref1) result: OK
Process 70 acquiring IS lock on OBJECT: 2:466816725:0  (class bit2000000 ref1) result: OK
Process 70 acquiring IS lock on PAGE: 2:5:168  (class bit2000000 ref0) result: OK
Process 70 acquiring S lock on RID: 2:5:168:0 (class bit2000000 ref0) result: OK
Process 70 acquiring IS lock on PAGE: 2:4:224  (class bit2000000 ref0) result: OK
Process 70 acquiring S lock on RID: 2:4:224:0 (class bit2000000 ref0) result: OK