--1 tran
BEGIN TRAN 

UPDATE dbo.P SET Id = 500
--COMMIT

--2 tran
BEGIN TRAN 
DECLARE @a INT = ( SELECT MAX(Id) FROM dbo.P )
UPDATE dbo.P SET Id = @a

COMMIT

create table test (
	id int not null primary key clustered
	, v int 
)

insert test(
	id
)
values (1), (3)



begin tran
set transaction isolation level read committed

update test with(rowlock) set 
	v = 1  
where 
	id = 2

exec sp_lock @@spid

commit



begin tran
set transaction isolation level serializable 
update test with(rowlock) set 
	v = 1  
where 
	id = 2

exec sp_lock @@spid

commit


drop table test