title: Combine two small queries (that group by different values) into one query
body: <p>Please take a look at the following table (called response). It shows what response a respondent has given to a question and answer.</p>
  
  <pre><code>questionid  answerid    respondentid
         1          10        1
         1          11        2
         1          11        4
         1          12        3
         1          12        5
         2          20        1
         2          20        2
         2          21        2
         2          22        1
         2          22        4
         2          23        1
         2          23        3
         2          24        4
         3          30        2
         3          30        3
         3          30        4
         3          31        1
  </code></pre>
  
  <p>We can run the following SQL:</p>
  
  <pre><code>select questionid, answerid, count(respondentid) as noOfRespondentsToQuestionAndAnswer
  from response
  group by questionid, answerid
  </code></pre>
  
  <p>... which will tell us how many respondents answered each combination of question+answer.</p>
  
  <p>We can also do:</p>
  
  <pre><code>select questionid, count(distinct respondentid) as noOfRespondentsToQuestion
  from response
  group by questionid
  </code></pre>
  
  <p>... which will tell us how many distinct respondents have answered each question.</p>
  
  <p>I would like to combine the two selects to ONE and let the number of distinct respondents be represented on more than one row for each questionid (which would be necessary, as it's only based on question and not also on answer).</p>
  
  <p>So, I would like a result like the following:</p>
  
  <pre><code>questionid,answerid,noOfRespondentsToQuestionAndAnswer,noOfRespondentsToQuestion
  1   10  1   5
  1   11  2   5
  1   12  2   5
  2   20  2   4
  2   21  1   4
  2   22  2   4
  2   23  2   4
  2   24  1   4
  3   30  3   4
  3   31  1   4
  </code></pre>
  
  <p>Is it possible to acheive this with just one query?</p>