Thanks again Jose. This will have a huge performance impact as its a material MD, and in future this might grow as the business increase. So as its a new development. I have added 0calmonth in the DSO and mapped 0date to the DSO. Now in the end routine where I am coding this select, can use the calmonth directly. No need to break the head.
Anyway thanks for the advise. Roy & Jose. Problem resolved.