-- ------------------------------------------------------
-- Example: What Customers Do NOT have shipping addresses
-- ------------------------------------------------------
select custid from customer
  where custid not in (select custid from soaddress)

-- -------------------------------------------------------
-- Example: What Projects exist in PjProj and not pjprojem
-- -------------------------------------------------------
select project from pjproj
  where project not in (select project from pjprojem)

-- Alternatively...
select project from pjproj
  where not (project in (select project from pjprojem))



-- --------------
-- Other Examples
-- --------------
SELECT count(*)
  FROM address
  WHERE addr_key NOT IN (SELECT addr_key FROM client)
     OR addr_key NOT IN (SELECT addr_key FROM employee)
     OR addr_key NOT IN (SELECT addr_key FROM groups)
     OR addr_key NOT IN (SELECT addr_key FROM patient)
     OR addr_key NOT IN (SELECT addr_key FROM provider)

-- Alternatively...
SELECT count(*)
  FROM address
  WHERE NOT (addr_key IN (SELECT addr_key FROM client)
        AND  addr_key IN (SELECT addr_key FROM employee)
        AND  addr_key IN (SELECT addr_key FROM groups)
        AND  addr_key IN (SELECT addr_key FROM patient)
        AND  addr_key IN (SELECT addr_key FROM provider))

-- Both of the above are logically the same but you should compare the
-- query plans for both and use the most efficient.