grouping and summing with sorting

[黄祥]

modules function

def report_vars_10(table_name, field_group, field_calc, query):

    table_field_group = current.db[table_name][field_group]

    table_field_calc = current.db[table_name][field_calc]

    table_field_sum = table_field_calc.sum()

    rows = current.db(query).select(table_field_group, table_field_sum, 

                                    groupby = table_field_group)

    grouping_calc = {}

    for row in rows:

        grouping_calc[row[table_name][field_group] ] = row[table_field_sum]

    return grouping_calc

objective

rows is sorted by table_field_sum, already tried :

using 

orderby = table_field_sum inside select()

result

no error occured but the result not expected

using

for row in rows.sort(lambda row: table_field_sum) 

result

(no error occured but the result not expected)

question

how to achieve it in web2py ?

thx