find and belongs_to

I have two tables

1)knowledge_bases

id integer not null default
nextval('public.knowledge_bases_id_seq'::text)
name character varying(200)
keyword text
url character varying(500)
summary text
details text

2)sd_knowledge_bases

id integer not null default
nextval('public.service_desk_knowledge_bases_id_seq
'::text)
sd_id integer
knowledge_base_id integer

In Sd
has_many :sd_knowledge_bases

In SdKnowledgeBase

belongs_to :sd
belongs_to :knowledge_base

For a given sd_id in sd_knowledge_bases table how can i find all the
fields from knowledge_bases table
Please help me

Sijo