SQL get names who didnt work on a project

Question

I would like to retrieve the names of people who didn\'t work on a project in PostgreSQL.

I got a table named employees with their names and

Answer 1

This is easy with NOT IN:

select * from employees
where ssn not in (select ssn from works_on)

Alternative with LEFT JOIN:

SELECT fname,lname
FROM employee w
LEFT JOIN works_on wa 
ON (wa.ssn = w.ssn)
WHERE wa.ssn IS NULL

This alternative is useful as you sometimes have more complicated requirements that can't easily be expressed with IN or EXISTS.