MySQL: Sort GROUP_CONCAT values

Sure, see http://dev.mysql.com/doc/refman/...tions.html#function_group-concat:

SELECT student_name,
  GROUP_CONCAT(DISTINCT test_score ORDER BY test_score DESC SEPARATOR ' ')
  FROM student
  GROUP BY student_name;

Do you mean to order by?

SELECT _key,            
COUNT(*) as cnt,            
GROUP_CONCAT(_value ORDER BY _value SEPARATOR ', ') as value_list      
FROM group_concat_test      
GROUP BY _key      
ORDER BY _key;