SELECT *
FROM (SELECT e.first_name||' '||e.last_name, e.SALARY, round((sysdate-e.hire_date)/365,2) STAJ, c.country_name FROM employees e, DEPARTMENTS d, LOCATIONS l, COUNTRIES c
WHERE round((sysdate-hire_date)/365,2)>=10
AND e.DEPARTMENT_ID=d.DEPARTMENT_ID
AND d.LOCATION_ID=l.LOCATION_ID
AND c.COUNTRY_ID=l.COUNTRY_ID
AND UPPER(c.country_name)=UPPER('United States of America')
ORDER BY e.SALARY DESC)
WHERE rownum <= 15
UNION ALL
(SELECT *
FROM (SELECT e.first_name||' '||e.last_name, e.SALARY, round((sysdate-e.hire_date)/365,2) STAJ, c.country_name FROM employees e, DEPARTMENTS d, LOCATIONS l, COUNTRIES c
WHERE round((sysdate-hire_date)/365,2)<10
AND e.DEPARTMENT_ID=d.DEPARTMENT_ID
AND d.LOCATION_ID=l.LOCATION_ID
AND c.COUNTRY_ID=l.COUNTRY_ID
AND UPPER(c.country_name)=UPPER('United States of America')
ORDER BY e.SALARY ASC)
WHERE rownum <= 15);