Remove group by field - group-by

Question

I've got an issue while getting data from DB2. I want to summarise the invoice amounts by customer. In one field, (calculated - I've called this InvoicedThisYear) it works out what was invoiced this year and in another it works out what was invoiced in the previous year (calculated, I've called it InvoicedLastYear). However, as it is summariesed I've grouped it by the Cust, but it is also wanting the data grouped by the InvoiceYear, so I've had to include this in the grouping. My problem is in my results I now have zeros for the years where there is no data and duplicates, e.g.:
Cust InvoicedThisYear InvoiceLastYear
abc 0 100
abc 100 0
Ideally I would like to see
Cust InvoicedThisYear InvoicedLastYear
abc 100 100
Here is my code:
SELECT
Cust AS Customer,
(CASE WHEN InvoiceYear = Year(Current Date) THEN sum(InvoiceAmt)ELSE 0 END) as InvoicedThisYear,
(CASE WHEN InvoiceYear = year(Current Date)-1 THEN sum(InvoiceAmt)ELSE 0 END) as InvoicedLastYear
FROM
InvHead
GROUP BY
Cust,
InvoiceYear
HAVING
((CASE WHEN InvoiceYear = Year(Current Date) THEN sum(InvoiceAmt)ELSE 0 END)<>0)
OR
((CASE WHEN InvoiceYear = year(Current Date)-1 THEN sum(InvoiceAmt)ELSE 0 END)<>0)
ORDER BY
Cust
How do I get the desired result? The query will not run if I remove the groupby Invoice Year
As a size note, it works in MS Access without grouping by the Invoice Year!
Thanks,
Michael

Answer 1

You need to put the SUM() around the case statements:
SELECT
Cust AS Customer,
sum(CASE WHEN InvoiceYear = Year(Current Date) THEN InvoiceAmt ELSE 0 END) as InvoicedThisYear,
sum(CASE WHEN InvoiceYear = year(Current Date)-1 THEN InvoiceAmt ELSE 0 END) as InvoicedLastYear
FROM
InvHead
GROUP BY
Cust
ORDER BY
Cust