SELECT COUNT(POK_cena) FROM POKOJE_GOSCINNE WHERE POK_cena = 100;

 DECLARE
 a NUMBER(32); b NUMBER(32);
 BEGIN
 SELECT COUNT(POK_cena) INTO a FROM POKOJE_GOSCINNE WHERE POK_cena = 100;
 --
 SELECT COUNT(POK_cena) INTO b FROM POKOJE_GOSCINNE;
 --
 dbms_output.put_line('Selektywnosc:'||TO_CHAR(a/b*100,'099D99999')||' [%]');
 END;
 /


 DECLARE
 a NUMBER(32); b NUMBER(32);
 BEGIN
 SELECT COUNT(POK_cena) INTO a FROM POKOJE_GOSCINNE WHERE POK_cena = 220;
 --
 SELECT COUNT(POK_cena) INTO b FROM POKOJE_GOSCINNE;
 --
 dbms_output.put_line('Selektywnosc:'||TO_CHAR(a/b*100,'099D99999')||' [%]');
 END;
 /


 SET timing ON;

 SELECT COUNT(POK_cena) FROM POKOJE_GOSCINNE WHERE POK_cena BETWEEN 100 AND 210;

 SELECT COUNT(POK_cena) FROM POKOJE_GOSCINNE WHERE POK_cena >= 100 AND POK_cena <= 210;

 SELECT COUNT(POK_cena) FROM POKOJE_GOSCINNE WHERE POK_cena > 90 AND POK_cena < 211;