title: How to return null values using SQL Left Join
body: <p>Please look at this SQL Fiddle for the tables and what query I have tried:<br>
  <a href="http://sqlfiddle.com/#!2/4c7b2/1" rel="noreferrer">SQL Fiddle</a>  </p>
  
  <p>So basically, I have two tables namely <strong>tbl_curriculum</strong> and <strong>tbl_enrolled_subjects</strong>.  </p>
  
  <p><strong>tbl_curriculum</strong> contains all the subjects (subject_id) a student should take based on his course (course_id).<br>
  <strong>tbl_enrolled_subjects</strong> contains all the subjects the student has taken/enrolled based on <strong>tbl_curriculum</strong>.  </p>
  
  <p>I want to check which subjects the student has taken and which is not, the query should return something like this:  </p>
  
  <pre><code>Subject_id|Grade|Status
  23        | 2   |Passed
  24        | 2   |Passed
  31        | 2   |Passed
  50        | 2   |Passed
  83        | 1   |Passed
  27        |NULL |NULL 
  28        |NULL |NULL 
  29        |NULL |NULL 
  </code></pre>
  
  <p>.
  .
  .
  And So On.</p>
  
  <p>Subject_ID with Grade and Status mean the student has already taken the subject. On the otherhand, NULL values indicates the the student has not taken those subjects yet.<br>
  I used this query:  </p>
  
  <pre><code>SELECT a.subject_id, b.grade, b.status
  FROM tbl_curriculum a
  LEFT JOIN tbl_enrolled_subjects b
  ON a.course_id = b.course_id  AND a.subject_id = b.subject_id
  WHERE b.student_id_no='05-0531';
  </code></pre>
  
  <p>But I keep getting only the subjects the student has taken.</p>
  
  <pre><code>Subject_id|Grade|Status
  23        | 2   |Passed
  24        | 2   |Passed
  31        | 2   |Passed
  50        | 2   |Passed
  83        | 1   |Passed
  </code></pre>
  
  <p>Am I missing something? Thanks in advance.</p>