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 usually solved using a NOT EXISTS query:

select e.*
from employees e
where not exists (select *
                  from works_on wo
                  where wo.ssn = e.ssn)

Answer 2

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.

Answer 3

try this

SELECT fname,lname
FROM werknemer w
WHere w.snn not in (Select wa.ssn from werkt_aan wa)

Answer 4

you'll need to use NOT IN and a subquery here