title: How to sort dates of three columns and get rows of all these rows?
body: <p>I have a MySQL table like this.</p>
  <pre><code>    |------------------------------------------------------------------------------|
      | NAME               |  DateType   |    date1    |     date2    |     date3    |
      |------------------------------------------------------------------------------|
      | Joe Bloggs         |  d1         |  21-09-2020 |  00-00-0000  |  00-00-0000  |
      | Bob Bobbing        |  d3         |  00-00-0000 |  23-11-2020  |  21-09-2010  |
      | etc... ----------------------------------------------------------------------|
  </code></pre>
  <p>What I want is, to merge these dates, sort them and get results like this:</p>
  <pre><code>|-------------------------------------------------|
  | NAME               |  DateType   |    date      |
  |-------------------------------------------------|
  | Joe Bloggs         |  d1         |  21-09-2020  |
  | Bob Bobbing        |  d3         |  23-11-2020  |
  | Bob Bobbing        |  d3         |  21-09-2010  |
  | etc... -----------------------------------------|
  </code></pre>
  <p>Or something like this, getting column name:</p>
  <pre><code>|----------------------------------------------------------------|
  | NAME               |  DateType   |   column     |    date      |
  |-------------------------------------------------|--------------|
  | Joe Bloggs         |  d1         |   date1      |  21-09-2020  |
  | Bob Bobbing        |  d2         |   date2      |  23-11-2020  |
  | Bob Bobbing        |  d3         |   date3      |  21-09-2010  |
  | etc... --------------------------------------------------------|
  </code></pre>