title: SQL Not Exists include null value
body: <p>I have two SQL Server tables :</p>
  
  <p>Table 1</p>
  
  <pre><code>Id name   description     version
  ----------------------------------
  1  Book1  Book 1 Title    v1
  2  Book2  Book 2 Title    v2
  3  Book3  Book 3 Title    NULL
  4  Book5  Book 5 Title    v3
  </code></pre>
  
  <p>Table 2</p>
  
  <pre><code>Id name   description     version
  ----------------------------------
  1  Book1  Book 1 Title    v1
  2  Book2  Book 2 Title    v2
  3  Book3  Book 3 Title    NULL
  4  Book4  Book 4 Title    NULL
  5  Book5  Book 5 Title    NULL
  </code></pre>
  
  <p>I want to select all data from table 2 that doesn't exist in table 1 so I can 
  insert them into another table.</p>
  
  <p>Here's the SQL query : </p>
  
  <pre><code>SELECT t2.name, t2.description, t2.version
  FROM Table2 AS t2
  WHERE  
      NOT EXISTS (SELECT t1.name, t1.description, t1.version 
                  FROM Table1 as t1 
                  WHERE t2.name = t1.name 
                    AND t2.description = t1.description  
                    AND t2.version = t1.version)
  </code></pre>
  
  <p>The result expected is this :</p>
  
  <pre><code>Id name   description     version
  -----------------------------------
  4  Book4  Book 4 Title    NULL
  5  Book5  Book 5 Title    NULL
  </code></pre>
  
  <p>But I'm getting this instead:</p>
  
  <pre><code>Id name   description     version
  ---------------------------------
  3  Book3  Book 3 Title    NULL
  4  Book4  Book 4 Title    NULL
  </code></pre>
  
  <p>Why the null value are not evaluated in my <code>NOT EXIST</code> statement and are displayed? </p>