Wrong query execution.

Hi,

It is possible that I am wrong, but I can nof find my mistake.

I have this 2 querie:

delete from a_grad where ids NOT in ( select KL.IDS_GRAD from
a_klienti kl ) ;

It returns 0 rows are deleted !

And the second one:

delete from a_grad where ids IN (select G.IDS FROM A_GRAD G WHERE NOT
EXISTS ( select * from a_klienti kl where KL.IDS_GRAD = G.IDS) ) ;

It returns 356 rows are deleted !

I expected that the first will delete also 356 rows.

I'm guessing this is the NULL issue hitting you. What does

SELECT ids_grad FROM a_klienti WHERE ids_grad IS NULL

show you?

For those interested, an example of the NULL vs IN issue can be seen in
the sample SQL below - just uncomment the 4th insert to tb.

DROP TABLE ta;
CREATE TABLE ta (id_a int4, a text);
DROP TABLE tb;
CREATE TABLE tb (id_b int4, id_a_ref int4);

INSERT INTO ta VALUES (1,'aaa');
INSERT INTO ta VALUES (2,'bbb');
INSERT INTO ta VALUES (3,'ccc');

INSERT INTO tb VALUES (1,1);
INSERT INTO tb VALUES (2,3);
INSERT INTO tb VALUES (3,1);
-- INSERT INTO tb VALUES (4,Null);

SELECT count(id_a) AS num_to_delete FROM ta WHERE id_a NOT IN (SELECT
id_a_ref FROM tb);
DELETE FROM ta WHERE id_a NOT IN (SELECT id_a_ref FROM tb);

HTH

- Richard Huxton

Hi Richard,
It is the case.
I have found records with NULL's !
Exist any docs where I can read more about interpreting of NOT IN ?

regards,
ivan.

dev@archonet.com wrote:

Hi Richard,
It is the case.
I have found records with NULL's !
Exist any docs where I can read more about interpreting of NOT IN ?

There's an item on it in my Postgresql Notes (subqueries and NULLs),
linked to from

http://techdocs.postgresql.org

You can also read more about it in Bruce's book (also available online
from the above URL).

Basically, any good relational database book should have a section of the
meaning of nulls.

- Richard Huxton

----- Original Message -----

Hi Richard,
It is the case.
I have found records with NULL's !
Exist any docs where I can read more about interpreting of NOT IN ?

There's an item on it in my Postgresql Notes (subqueries and NULLs),
linked to from

http://techdocs.postgresql.org

You can also read more about it in Bruce's book (also available online
from the above URL).

Basically, any good relational database book should have a section of the
meaning of nulls.

And why they shouldn't be allowed in a database. ;-)

Mike Mascari
mascarm@mascari.com