DELETE FROM firmalar
USING firmalar, firmalar as firmalarx
WHERE (firmalar.id = firmalarx.id)
AND (firmalar.firma_adi=firmalarx.firma_adi) AND (firmalar.firma_il=firmalarx.firma_il)
AND (firmalar.firma_adresi=firmalarx.firma_adresi) ;

select count(*) from firmalar;