--finding most frequent occupation for each education level group
SELECT  educationlevel, educationnumeric, occupation, count(*)
FROM person P
GROUP BY educationlevel,educationnumeric, occupation
HAVING COUNT(*)=(SELECT MAX(cnt) FROM
                    (SELECT educationlevel, occupation, count(*) as cnt
                    FROM person
                    GROUP BY occupation, educationlevel) count_table
                WHERE P.educationlevel = count_table.educationlevel)
ORDER BY 2;