SQL selection join help

Question

I'm having problems figuring out a query for this scenario. I have two tables I want to use in this query, they are like this:

Units
  ID
  Other Data
People
  ID
  UnitID  <-- fk to Units
  Other Data

This is what I want to do:
I want to select all the units that do NOT have a row in the People table linked to them. How can I do this?

Answer 1

SELECT Units.* FROM Units LEFT JOIN People ON People.UnitID = Units.ID WHERE People.ID IS NULL

or alternatively

SELECT Units.* FROM Units WHERE NOT EXISTS (SELECT 1 FROM People WHERE People.UnitID = Units.ID)

or even

SELECT Units.* FROM Units WHERE Units.ID NOT IN (SELECT UnitID FROM People)

Answer 2

SELECT * FROM Units  
WHERE NOT EXISTS  
(SELECT * FROM People WHERE UnitID = Units.ID)