SQL Method to report next period value for this period - sql

Question

This may already be answered, but I can't figure out the correct search terms for what I need. We store values by Year / Period for the Beginning of Month (BOM). The BOM for one month is the same value as End of Month (EOM) for the previous month. I need a way to report this as such.
So 2018-02 BOM = 2018-01 EOM.
I thought I might be able to use something simple, but it does not account for the month/year wrap at 12 months as those fields are numerical.
select yr as YEAR, (pd-1) as PERIOD, sum(BOM) as EOM
from Table1
where type = '3'
group by yr, pd
order by yr desc, pd desc
This works for the middle months, but not for January, which becomes 2018-0 instead of 2017-12.
Example Data
Yr Pd Type BOM
18 02 3 100
18 02 3 100
18 02 2 200
18 02 2 100
18 01 3 100
18 01 3 100
18 01 2 200
18 01 2 100
18 01 3 100
18 01 2 300
17 12 3 100
17 12 3 200
17 12 2 300
17 12 3 200
17 12 2 100
17 11 3 300
17 11 2 400
17 11 3 400
17 11 2 100
So the results I am looking for would be:
Yr Pd EOM
18 01 200
17 12 300
17 11 500
17 10 700
I'm working in System iNavigator currently, but hoping to move this into an externally connected Excel query at some point.

Answer 1

Your DB2 database should be able to use CASE WHEN
Which can be used to calculate the year and the month, depending on the month.
For example:
select
CASE WHEN pd = 1 THEN yr - 1 ELSE yr END as Yr,
CASE WHEN pd = 1 THEN 12 ELSE pd - 1 END as Pd,
SUM(BOM) as EOM
from Table1
where type = '3'
group by yr, pd
order by yr desc, pd desc