How to calculate accumulated deprciation

Hi ,

I am calculating accumulated depriciation and NBV .I am using the following query .But for each asset there are multiple rows available .I need  one row which i will show in my report.

select (fds.deprn_reserve) accumulated_depriciation,(fb.cost-fds.deprn_reserve)NBV

from fa_books fb,

fa_deprn_summary fds

where fb.asset_id=fds.asset_id

and fb.book_type_code=fds.book_type_code

and fds.ASSET_ID=fb.asset_id

and fb.date_ineffective is null

and fb.ASSET_ID=input_assetid

How i will filter the other rows?..probably they are available because multiple time depriciation has run...