I don't understand...

Hi All ,

SELECT DISTINCT h_name FROM haszon;
+---------------+
| h_name |
+---------------+
| CITROEN |
| DAEWOO-FSO |
| DAEWOO-LUBLIN |
| FIAT |
| FORD |
| GAZ |
| HYUNDAI |
| KIA |
| MAZDA |
| MERCEDES BENZ |
| MITSUBISHI |
| NISSAN |
| OPEL |
| PEUGEOT |
| RENAULT |
| SEAT |
| SKODA |
| SUZUKI |
| TATA |
| TOYOTA |
| VOLKSWAGEN |
+---------------+
Query OK, 21 rows in set (0,20 sec)

SELECT cn_name FROM carname

+---------------+
| cn_name |
+---------------+
| ALFA ROMEO |
| AUDI |
| BMW |
| CHRYSLER |
| CITROEN |
| DAEWOO |
| DAIHATSU |
| DAIMLER |
| FIAT |
| FORD |
| HONDA |
| HYUNDAI |
| JAGUAR |
| JEEP |
| KIA |
| LADA |
| LANCIA |
| LAND ROVER |
| LEXUS |
| MAZDA |
| MERCEDES BENZ |
| MG |
| MITSUBISHI |
| NISSAN |
| OPEL |
| PEUGEOT |
| PORSCHE |
| PROTON |
| RENAULT |
| ROVER |
| SAAB |
| SEAT |
| SKODA |
| SUBARU |
| SUZUKI |
| TOYOTA |
| VOLKSWAGEN |
| VOLVO |
| <Null> |
+---------------+
Query OK, 39 rows in set (0,35 sec)

SELECT DISTINCT h_name
FROM haszon
WHERE h_name IN (SELECT cn_name FROM carname)

+---------------+
| h_name |
+---------------+
| CITROEN |
| FIAT |
| FORD |
| HYUNDAI |
| KIA |
| MAZDA |
| MERCEDES BENZ |
| MITSUBISHI |
| NISSAN |
| OPEL |
| PEUGEOT |
| RENAULT |
| SEAT |
| SKODA |
| SUZUKI |
| TOYOTA |
| VOLKSWAGEN |
+---------------+
Query OK, 17 rows in set (0,22 sec)

I think it's good, but
SELECT DISTINCT h_name
FROM haszon
WHERE h_name NOT IN (SELECT cn_name FROM carname)

+--------+
| h_name |
+--------+
+--------+
Query OK, 0 rows in set (0,10 sec)

Why ?

postgres-7.1 rpm on RedHat 7.0

Thanks, Gabor