why can't i use "where R.ApartmentID = null" to retrieve all non matching rows from the left table : I only have a month of learning experience on sql server and I was just wondering why the first query before produces the right results (i.e. join two table and only select rows from left table that does NOT have a matching row), whereas the second query returns an empty query. 

First

    select R.Name, A.Name
    from tblResident as R 
    left join tblApartment as A
    on R.ApartmentID = A.ID
    where R.ApartmentID is null

Second 

    select R.Name, A.Name
    from tblResident as R 
    left join tblApartment as A
    on R.ApartmentID = A.ID
    where R.ApartmentID = null

Table structure 

[![enter image description here][1]][1]


  [1]: http://i.stack.imgur.com/8Km5G.png