title: SQL query with "group by with cube" and NULL values
body: <p>I have a table like:</p>
  
  <pre><code>+------+------+------+
  | col1 | col2 | col3 |
  +------+------+------+
  | A    | 1    | foo  |
  | A    | 1    | foo  |
  | A    | 2    | foo  |
  | B    | 1    | foo  |
  | B    | 2    | foo  |
  | B    | NULL | foo  |
  | NULL | 1    | foo  |
  +------+------+------+
  </code></pre>
  
  <p>I want to see numbers of <code>foo</code> grouped by <code>col1</code> and <code>col2</code>:</p>
  
  <pre><code>+-------+---+---+------+-------+
  |       | A | B | NULL | TOTAL |
  +-------+---+---+------+-------+
  | 1     | 2 | 1 |    1 |     4 |
  | 2     | 1 | 1 |    0 |     2 |
  | NULL  | 0 | 1 |    0 |     1 |
  | TOTAL | 3 | 3 |    1 |     7 |
  +-------+---+---+------+-------+
  </code></pre>
  
  <p>I use a query like this:</p>
  
  <pre><code>select 
      col1,
      col2,
      count(col3)
  from table
  group by 
      col1,
      col2 
  with cube
  </code></pre>
  
  <p>And I have 4 rows with <code>col1</code>, <code>col2</code> and <code>NULL</code> that say for <code>NULL/NULL</code>, <code>NULL/TOTAL</code>, <code>TOTAL/NULL</code>, <code>TOTAL/TOTAL</code> but the totals for sql has <code>NULL</code> value.</p>
  
  <p>Is possible set a custom value different from <code>NULL</code> for the totals in the query?</p>