SQL> create table tab1 ( i1 int );
Table created.

SQL> create table tab2 ( i2 int );
Table created.

SQL> select * from tab2 where i2 not in ( select i2 from tab1 );
no rows selected

SQL> disc
Disconnected from Oracle9i Enterprise Edition Release 9.2.0.8.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.8.0 - Production

$ psql -U zabbixuser zabbix
Password for user zabbixuser: 
Welcome to psql 8.3.1, the PostgreSQL interactive terminal.

zabbix=> create table tab1 ( i1 int );
CREATE TABLE
zabbix=> create table tab2 ( i2 int );
CREATE TABLE
zabbix=> select * from tab2 where i2 not in ( select i2 from tab1 );
 i2 
----
(0 rows)

$ mysql zabbix
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 449695
Server version: 5.0.51a-log SUSE MySQL RPM

mysql> create table tab1 ( i1 int );
Query OK, 0 rows affected (0.14 sec)

mysql> create table tab2 ( i2 int );
Query OK, 0 rows affected (0.07 sec)

mysql> select * from tab2 where i2 not in ( select i2 from tab1 );
Empty set (0.09 sec)