How Can I Fix My Decode and Mod Code In The SQL

Question

I have the following SQL statement.
SELECT BEG_SVC_DT, END_SVC_DT,
DECODE((SUBSTR(END_SVC_DT,5,2) - SUBSTR(BEG_SVC_DT,1,2)+1),30,mod(trunc(months_between((to_date('20'||end_svc_dt,'YYYYMMDD')),BEG_SVC_DT)),12)+ 1,
mod(trunc(months_between((to_date('20'||end_svc_dt,'YYYYMMDD')),BEG_SVC_DT)),12))
FROM SVC_OCCURRENCES
WHERE SUBSTR(END_SVC_DT,1,1) IN '0'
AND SUBSTR(END_SVC_DT,5,2) NOT IN ('31')
Now if the decode returns a value of '30' then 1 is added to the remainder using
the MOD function otherwise the MOD function is used and 1 is not added which is
alright.
After a '1' is added to the remainder , a value of '1','2','3','4', '5','6','7','8','9','10','11','12' is obtained which is alright also.
However I do not want a '12' to appear instead I want a '0' (zero) to appear. Can I do this in an SQL statement? Eventually I want to do this in a report.

Answer 1

SELECT BEG_SVC_DT, END_SVC_DT ,
DECODE(
(SUBSTR(END_SVC_DT,5,2) - SUBSTR(BEG_SVC_DT,5,2)+1),30,
mod(trunc(months_between(add_months(to_date('20'||end_svc_dt,'YYYYMMDD'),1),to_date('20'||BEG_SVC_DT,'yyyymmdd'))),12),
mod(trunc(months_between((to_date('20'||end_svc_dt,'YYYYMMDD')),to_date('20'||BEG_SVC_DT,'yyyymmdd'))),12))
FROM SVC_OCCURRENCES
WHERE SUBSTR(END_SVC_DT,1,1) IN '0'
AND SUBSTR(END_SVC_DT,5,2) NOT IN ('31')
Hope this Helps
Stan