DECODE output may be type sensitive

Assuming current months is MAY

Since MM format will return ’05’ it won’t match ‘5’ as shown below

select decode(to_char(sysdate,'MM'),'05','MAY','other month') from dual; --MAY
select decode(to_char(sysdate,'MM'),'5','MAY','other month') from dual; -- other month

At the same time, if 05 or 5 will be used with decode instead of ’05’ or ‘5’ then both queries will give us the same result. It is happening because Oracle will implicitly adjust between character and numeric data types in this case.

select decode(to_char(sysdate,'MM'),05,'MAY','other month') from dual; --MAY
select decode(to_char(sysdate,'MM'),5,'MAY','other month') from dual; --MAY