Informix CASE and summing results - subquery

Question

I have finally joined after many month of always getting my answer from here without having to ask but rather simply searching on here :).
I am fairly new to Informix and am struggling with my first CASE statement:
The rough idea of it is that I am awarding points based on revenue for a rewards program and two months in there are double point months.
My Select looks something like this:
Select YearMonth,
Account_Number,
Customer_Name,
Gross_Revenue,
Gross_Revenue * BLC_multiplier BLC_Points
from (
Select salesstat.year_num||salesstat.int_num YearMonth,
Customer.cust_code Account_Number,
Customer.name_text Customer_Name,
sum(salesstat.net_amt-salesstat.return_net_amt) Gross_Revenue,
CASE
WHEN
salesstat.int_num in (4,8)
THEN
.02
ELSE
.01
END BLC_multiplier
from Customer,
salesstat,
warereptdetl,
Product,
maingrp
Where product.cmpy_code = 'AB'
and Product.part_code = salesstat.part_code
and salesstat.cmpy_code = 'AB'
and customer.cmpy_code = 'AB'
and customer.cust_code = salesstat.cust_code
and salesstat.rept_code = '0'
and warereptdetl.ware_code = salesstat.ware_code
and warereptdetl.cmpy_code = 'AB'
and salesstat.year_num||salesstat.int_num in ('201412','20151','20152','20153','20154','20155','20156','20157','20158','20159')
and salesstat.ord_ind in ('7','8')
and salesstat.stat_type_code = 'MLY'
and salesstat.int_num > 0
and warereptdetl.warereptgrp_code in('NSW','MNW')
and maingrp.maingrp_code = salesstat.maingrp_code
and maingrp.cmpy_code = 'AB'
and customer.ref6_code = 'BLC'
and customer.ref7_code in ('Y','U')
and customer.cust_code in ('408759','112348')
group by YearMonth,
Customer.cust_code,
Customer.name_text,
BLC_multiplier
Order by YearMonth asc,
Customer.cust_code asc
)
I wanted to do it all in one go something like:
Select salesstat.int_num MonthValue,
sum(salesstat.net_amt-salesstat.return_net_amt) Gross_Revenue,
sum(salesstat.net_amt-salesstat.return_net_amt) *
CASE
WHEN
salesstat.int_num in (4,8)
THEN
.02
ELSE
.01
END BLC_Points
but when I do it tells me that BLC_Points needs to be in the group by (which it can't because it is an aggregate field)
I also tried:
Select salesstat.int_num MonthValue,
sum(salesstat.net_amt-salesstat.return_net_amt) Gross_Revenue,
CASE
WHEN
salesstat.int_num in (4,8)
THEN
sum(salesstat.net_amt-salesstat.return_net_amt) * .02
ELSE
sum(salesstat.net_amt-salesstat.return_net_amt) * .01
END BLC_Points
Whilst my fix DOES WORK, I want to make sure I am doing it properly. Incorrect code is hard to maintain.

Answer 1

I note JL's comments in your question, and agree that is all very good advice.
Long story short, you cannot use labels/aliases for columns or expressions in the GROUP BY clause. The simple solution is to use the ordinal position alternative: GROUP BY 1, 2, 3, 4
For what it's worth, an alternative to the CASE statement that I prefer for legibility would be:
DECODE(salesstat.int_num,
4, 0.2
8, 0.2
0.1) AS BLC_Points
(Do with that last bit as you please.)