title: SQL count values in different columns with date range
body: <p>I know how to count values in different columns and with date ranges, but not when I have to do both things in the same time.</p>
  
  <p>I have table with this example values:   </p>
  
  <pre><code>   DATE    | Number1 | Number2 | Number3 | Number4 | Number5 | Number6  
  2017-08-05 |   01    |   02    |   03    |   04    |    05   |   06
  2017-08-04 |   02    |   03    |   04    |   05    |    06   |   07
  2017-08-03 |   03    |   04    |   05    |   06    |    07   |   08
  2017-08-02 |   04    |   05    |   06    |   07    |    08   |   09
  2017-08-01 |   05    |   06    |   07    |   08    |    09   |   10
  </code></pre>
  
  <p>And now i want to have result like this for choosen data range (ex. from 2017-08-02 to 2017-08-03):  </p>
  
  <pre><code>Number | occurrences
    03   |     1
    04   |     2
    05   |     2
    06   |     2
    07   |     2
    08   |     2
    09   |     1
  </code></pre>
  
  <p>How to do this in one SQL query?</p>