How can I order a selection by the results of a function (sum)?

Question

I have a table with a bunch of columns. Three columns are integers, and are labeled consumption, consumption2, and consumption3.

I would like to select each full row of the table, but order the selection by the sum of the three consumption fields descending.

I can order by each consumption column individually

order by consumption3 desc, consumption 2 desc, consumption desc

but I would prefer to sum these values and then order by that summed value.

I can also write a 4GL program to do this, but am trying to solve this in SQL.

If I do this,

select  *
from    ws_bill
order by sum(consumption) + sum(consumption2) + sum(consumption3)

then Informix's SQL wants every column in the group by list.

Is there an easier way to do this, or should I just write the program?

Versions of Informix SE/4GL running on Ubuntu 12.04

ics@steamboy:~/icsdev$ dbaccess -V
DB-Access Version 7.25.UC6R1 
Software Serial Number ACP#J267193
ics@steamboy:~/icsdev$ fglpc -V

Pcode Version 732-750

Software Serial Number ACP#J267193
ics@steamboy:~/icsdev$ 

Here is the table:

create table "ics".ws_bill 
  (
    yr char(2),
    bill_no integer,
    bill_month smallint,
    due_date date,
    tran_date date,
    prev_reading integer,
    curr_reading integer,
    consumption integer,
    consumption2 integer,
    consumption3 integer,
    water_charge money(10,2),
    sewer_charge money(10,2),
    other_charge decimal(10,2),
    curr_bal money(10,2),
    estimated char(1),
    prev_due_date date,
    time_billed datetime year to second,
    override char(1),
    curr_bal_save money(10,2)
  );
revoke all on "ics".ws_bill from "public";

create unique index "ics".ws_indx on "ics".ws_bill (bill_no,yr,
    bill_month);

---

This is the main cursor as denoted in the accepted answer for this post.

declare wb_cp cursor for
select  b.yr,b.bill_no,
        sum(b.consumption + b.consumption2 + b.consumption3) as adj_tot
into    cons_rec.* #defined record variable
from    ws_bill b
where   b.yr >= start_yearG and b.yr <= end_yearG
group   by b.yr, b.bill_no
order by adj_tot desc, b.yr desc, b.bill_no desc

Answer 1

You are talking about summing three columns. This is a simple expression (consumption + consumption2 + consumption3). You do not need the sum(...) function unless you want to sum multiple rows that you are grouping together.

So, you need something along these lines:

select bill_no, bill_month, ..., (consumption + consumption2 + consumption3) as tot_sum
  from ws_bill
 order by tot_sum desc