左连接替代not exists

asset_id is primary key. 

insert b
select asset_id, cusip, 'G' from a
where  not exists ( select * from b
                    where b.asset_id = a.asset_id )

insert b
select a.asset_id, a.cusip, 'G'
from a left join b
on a.asset_id = b.asset_id
where b.asset_id is NULL