NOT EXISTS - not working

Question

Dear all,
I have 3 tables say A1000, B1000, C1000
create table A1000(a number);
create table B1000(a number);
create table C1000(a number);
With below values:
insert into A1000 values(1)
insert into B1000 values(1)
insert into C1000 values(2)
My Query:
SELECT a.a FROM a1000 a, b1000 b
WHERE a.a=b.a
AND NOT EXISTS (SELECT a FROM C1000)
Since both the tables a1000 & b1000 has matching records, I am expceting one row from A1000. But the query is not returning any row.
Even though table C1000 has one record with value as 2, it should not affect the result set right?
Regards
Natarajan M

Answer 1

it should not affect the result set right?Right, when you tell Oracle the right thing:
SQL> select a.a
  2  from   a1000 a
  3  ,      b1000 b
  4  where  a.a = b.a
  5  and not exists ( select null   --< don't select anything here
  6                   from   c1000 c
  7                   where  c.a = a.a
  8                 );
         A
         1
1 row selected.The fact that you selected 'a' (without any alias) makes me think you treat EXISTS a bit like IN, but they differ.
See:
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:442029737684
http://asktom.oracle.com/pls/asktom/f?p=100:11:3637710709480187::::P11_QUESTION_ID:953229842074
for (much) more information