title: left join not showing null values
body: <p>I need to find the items that exist in table A but not in table B. Now that would be really simple in MySQL doing a join like this</p>
  
  <pre><code>select * from A 
  left join B on A.key=B.key 
  where B.key is null
  </code></pre>
  
  <p>However for some reason this is not working in MSSQL. I have created the query without the where clause to see all the results and I only see matches, not null values. Do you have any idea why this is not working? </p>
  
  <p>I know I can alternatively use "when not exists" but I want to know the reason as to why with a join is not working.</p>
  
  <p>I am adding the code for your review</p>
  
  <pre><code>select Absences.CustomerID, b.* 
  from (
      select * from openquery(JUAN_INTERFACE,'select cmp_wwn from Planet_Customers where   i_outcome =4')) b 
  left join Absences on Absences.CustomerID = b.cmp_wwn 
  where Absences.Type = 3223
  </code></pre>