title: UNION ALL with unknown column value
body: <p>Hello I have a working SELECT that uses UNION ALL to return 0 values, however I'm not sure how to add another column to the UNION that has an unknown value:</p>
  
  <pre><code>SELECT status, type, company
      ROW_NUMBER() OVER (PARTITION BY title ORDER BY id) As RowNumber
  FROM table
  WHERE type IN ('type1', 'type2', 'type3') AND
      status IN ('status1', 'status2', 'status3')
  
  /* issue starts here */
  UNION ALL SELECT 'status1', 'type1', null, 1
  UNION ALL SELECT 'status2', 'type1', null, 1
  UNION ALL SELECT 'status3', 'type1', null, 1
  
  /*                                    ^ unknown value */
  
  /* ... repeat for all status * type combinations */
  </code></pre>
  
  <p>RowNumber is used to find the first occurrence of a title in the parent SELECT(not shown).</p>
  
  <p>The expected end result is placed in another query in the FROM clause to do a count:</p>
  
  <pre><code>--------------------------------------
  | status   | type  | company | count |
  --------------------------------------
  | status1  | type1 | abc     | 1     |
  | status2  | type1 | abc     | 24    |
  | status3  | type1 | abc     | 0     |
  --------------------------------------
  </code></pre>
  
  <p>As you can see I tried NULL for the company in the UNION ALL, this doesn't work is there a way to "use" the values found in the "company" column?</p>
  
  <p>Thanks.</p>