select NOT IN with NULL bug on 7.2b3
Hi,
it is a bug ??
create table test (t1 int4, t2 int4);
insert into test values (1,1);
insert into test values (2,2);
insert into test values (3,1);
insert into test values (4,1);
insert into test values (4,1);
insert into test values (4,null);
select * from test where t1 not in (select t2 from test);
0 rows
select * from test where t1 not in (select null);
0 rows
If I delete the row with null value it works as expected.
The IN clause work as expected with or without null row.
sorry for my english.
bye
--
-------------------------------------------------------
Giuseppe Tanzilli g.tanzilli@gruppocsf.com
CSF Sistemi srl phone ++39 0775 7771
Via del Ciavattino
Anagni FR
Italy
On Thu, 29 Nov 2001, Giuseppe Tanzilli - CSF wrote:
Hi,
it is a bug ??create table test (t1 int4, t2 int4);
insert into test values (1,1);
insert into test values (2,2);
insert into test values (3,1);
insert into test values (4,1);
insert into test values (4,1);
insert into test values (4,null);select * from test where t1 not in (select t2 from test);
0 rows
select * from test where t1 not in (select null);
0 rowsIf I delete the row with null value it works as expected.
The IN clause work as expected with or without null row.
I think this falls into the nulls are painful category of
trivalued logic.
IIRC:
When you ask for t1 not in (subselect)
you get : not(t1 in (subselect) -> not(t1 =ANY (subselect))
-> for each row of subselect does t1 = t2 (in your case)
* if true for any row, the in returns true (not in returns false)
* if false for every row, the in returns false (not in - true)
* otherwise, the in returns unknown (not in - also unknown).
Basically with a NULL, you can say that a row is there definitively
but not that a row is not there since you don't know if the 3 equals
that NULL or not (same for the 4s).
