สอบถามปัญหาคำสั่ง SQL ของ MySQL เกี่ยวกับการใช้ Groupby 2 คอลัม ครับ

SELECT
visit.visitno,
ctitle.titlename,
person.fname,
person.lname,
getAgeYearNum(birth,curdate()) AS AGE,
person.idcard,
person.sex,
visit.visitdate,
visitdiag.diagcode,
cdrug.drugname
FROM
visit
INNER JOIN visitdiag ON visit.visitno = visitdiag.visitno
INNER JOIN visitdrug ON visitdiag.visitno = visitdrug.visitno
INNER JOIN cdrug ON visitdrug.drugcode = cdrug.drugcode
INNER JOIN person ON person.pid = visit.pid
INNER JOIN ctitle ON person.prename = ctitle.titlecode
WHERE
visit.visitdate BETWEEN '2013-01-01' AND '2013-01-31' AND
visit.hossub = 11924
GROUP BY diagcode
ORDER BY visitno