SQL select where value not matched

Question

I have 2 tables. One is people with name, ssn, etc. The other is cars with ssn, make, model, etc.

How would I go about selecting from the people table where the ssn column doesn't match with any ssn from the cars table?

The combined table has ssn, name, etc, carssn, carid , and anyone that doesn't have a ssn on the cars table has NULL for those 2 columns when the tables are joined.

Answer 1

I would use not exists :

select p.*
from people p
where not exists (select 1 from cars c where c.ssn = p.ssn);

Answer 2

I would use not in :

select *
from people
where ssn not in (select ssn from cars);

If you want to use a join, as described in the question, use is null :

select p.*
from people p
left join cars c using (ssn)
where c.ssn is null;

Answer 3

It is possible to use ALL as well

select *
from people
where ssn != ALL(select ssn from cars);

if ssn in cars is never NULL . If ssn is sometimes NULL than you might use

select *
from people
where ssn != ALL(select ssn from cars where ssn IS NOT NULL);

You should worry about NULL s also in solution using NOT IN