SQL: Aggregate within in aggregate?

In Informix SE 7.23, 4GL 6.04 How can I in effect nest an aggreate like SELECT MAX(SUM(column)) where.....? If I have a table contract char(3) grade char (1) amount integer For a given contact I want to select the grade having the MAX of SUM(amount) So if my data is: contract grade amount XYZ A 20 XYZ B 20 XYZ B 19 XYZ A 21 XYZ C 30 I want the SQL statement to return me the grade value of "A" since the SUM(amount) of all A grade rows is 41 and the SUM(amount) of all B grade rows is 39 and C = 30 Please help me with the syntax. Thanks in advance Matt Brickley