Multiple SELECT with NOT IN - inner Select statement returns empty and the whole SELECT returns empty

Question

There are two table TABLE1 and TABLE2 in which there is a common field ID. I wanted to retrieve values from TABLE2 that doesnot match in TABLE1 based on ID value.

select * from TABLE2 where subject = 1 and ID NOT IN (select ID from TABLE1 where subject = 1)

Sample:

TABLE1
ID SUBJECT
1 1

TABLE2
ID SUBJECT
1 1
2 1

The expected result is 2 and it works fine.

But when TABLE1 is empty or the inner select ID from TABLE1 where subject = 1 returns empty, the whole select statement returns empty. But the expected result is 1, 2

Is there any way to achieve this ?

Answer 1

Use a left join

select t2.* 
from table2 t2
left outer join table1 t1 on t1.id = t2.id and t1.subject = 1
where t2.subject = 1
and t1.id is null

See a good explanation of joins

Answer 2

I think you can use not exists also for this work -

select * from TABLE2 where subject = 1 and NOT exists
(select 1 from TABLE1 where subject = 1 and table1.id = table2.id)