Alternative To Subselect Query

Hi,

Hope someone could help me in revising a long running query. Here is the query

select *
from table1
where classid is null
and productid not in (
select productid
from table1
where classid = 67)

In here table1 could have several occurance of productid in which productid could have different classid. The possible values of classid are: NULL,1,2,3,67. Basically I am looking for all records whose classid is null but should never had an instance in table1 where its classid is 67.

Do you have something like a "join" statment that will only include all records in the left table that is not in the right table?

Hope someone could help me with this. Thanks in advance.

-Ruel