NOT IN with NULL-values

From: Kuijten, F. (Frank) <f.kuijten_at_organonteknika.nl>
Date: Mon, 29 Oct 2001 00:42:04 -0800
Message-ID: <F001.003B6B5C.20011029004517@fatcity.com>

Hello,

I'm running the SQL-statements below :

SQL> create table fk_ldm1 (id number(10) not null); Table created.
SQL> insert into fk_ldm1 values(1);
1 row created.
SQL> insert into fk_ldm1 values(2);
1 row created.
SQL> insert into fk_ldm1 values(3);
1 row created.
SQL> insert into fk_ldm1 values(4);
1 row created.

SQL> create table fk_ldm2 (id number(10)); Table created.
SQL> insert into fk_ldm2 values(1);
1 row created.
SQL> insert into fk_ldm2 values(2);
1 row created.
SQL> insert into fk_ldm2 values(4);
1 row created.
SQL> insert into fk_ldm2 values(NULL);
1 row created.

As you can see, value '3' is not in 'fk_ldm2' and value 'NULL' is not in 'fk_ldm1'.

Now for the following selects :
SQL> select * from fk_ldm1
  2 minus
  3 select * from fk_ldm2;

       ID

---

        3

SQL> select * from fk_ldm1
  2 where id not in (select * from fk_ldm2); no rows selected

SQL> select * from fk_ldm1
  2 where not exists (select * from fk_ldm2); no rows selected

SQL> select * from fk_ldm1
  2 where id not in (select * from fk_ldm2 where id is not null);

       ID

---

        3

I had expected to see value '3' appear in all selects. It has something to do with the NULL value in 'fk_ldm2', but I've got no explanation for this.

Why won't value '3' appear as soon as a NULL value is used ???

(It's not a bug as this behaviour is the same in 7.1.5, 8.0.6 and 8.1.6)

Greetings,
Frank

---

Frank Kuijten
DBA/Developer
Organon Teknika bv
P.O. Box 84
5280 AB Boxtel
Republic of The Netherlands
+31 411 654265
f.kuijten_at_organonteknika.nl

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Author: Kuijten, F. (Frank)
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Received on Mon Oct 29 2001 - 02:42:04 CST