why this query is faling?

Question

select max( sum(duration) ),cd from rent group by cd; 

.

ERROR 1111 (HY000): Invalid use of group function

Answer 1

From documentation - group (aggregate) functions that operate on sets of values.. SUM returns scalar value.

Is this what you want?

SELECT MAX(duration_sum_by_cd) FROM (
  SELECT SUM(duration) duration_sum_by_cd FROM rent 
    GROUP BY cd; 
) t