title: MySQL Left Join not returning null values for joined table
body: <p>Please help me with the following MySQL query, which joins two tables (A and B):</p>
  
  <pre><code>SELECT * from A
  left join B on A.sid = B.sid
  where (rCode = 1 Or rCode = 2 Or rCode = 3 Or rCode = 5)
  AND (rYear = 2011 or rYear is null)
  </code></pre>
  
  <p><code>roleCode</code> is a field in table A and <code>rYear</code> is a field in table B</p>
  
  <p>The result set is not as expected. Only 185 rows are returned, but there are 629 rows in table A that match the where condition. Shouldn't the rows without a matching row in table B be returned with null values for their B fields?</p>