title: merge two datasets with datatable but keeping one of the identical column
body: <p>Havent found this one yet so here we go.
  I am using datatables and I want to merge two tables that differn in length.
  Ich have done that successfully.</p>
  <p>So basically I merge all rows where my key attribute &quot;Name, Date1&quot; from my table1 is euqal to my key attribute &quot;Name, Date2&quot; from my table 2.</p>
  <p>The problem I got with this, that my Date2 from my table 2 disapperas.
  I do not like that. I want to keep my date2 from my table 2.</p>
  <p>Example:</p>
  <p>Table1</p>
  <pre><code>Name   Date1
  A      2018-01-01
  A      2018-01-02
  A      2018-01-03
  </code></pre>
  <p>Table2</p>
  <pre><code>Name   Date2
  A      2018-01-01
  A      2018-01-02
  A      2018-01-15
  </code></pre>
  <p>Instead of looking like this in my</p>
  <p>New table</p>
  <pre><code>Name   Date
  A      2018-01-01
  A      2018-01-02
  A      NA
  </code></pre>
  <p>it should look like this</p>
  <pre><code>Name   Date1         Date2
  A      2018-01-01    2018-01-01
  A      2018-01-02    2018-01-02
  A      NA            NA
  </code></pre>
  <p>Does anyone know the trick?</p>