--Mode education for each occupation group
SELECT freqeducation.worktype, freqeducation.educationlevel, freqeducation.cnt
FROM 
     (SELECT worktype,
        educationlevel,               
        COUNT(*) as cnt
        FROM person
        GROUP BY worktype, educationlevel
     ) freqeducation JOIN
     (SELECT worktype, MAX(cnt) as maxcnt
        FROM (SELECT worktype, educationlevel, COUNT(*) as cnt
                FROM person 
                GROUP BY worktype, educationlevel) c
        GROUP BY worktype
     ) educationmax
     ON freqeducation.worktype = educationmax.worktype AND freqeducation.cnt = educationmax.maxcnt        
ORDER BY 1, 2;