title: Azure Data Factory / Aggregate as comma separated string
body: <p>I want to aggregate by data using <code>Aggregate</code>. </p>
  
  <p>Here is the scenario:</p>
  
  <p>I've a table having values as below:</p>
  
  <pre><code>Key | Value
  1   | v1
  1   | v2
  2   | v1
  2   | v3
  </code></pre>
  
  <p>After performing aggregation, I want output as below:</p>
  
  <pre><code>Key | Value
  1   | v1, v2
  2   | v1, v3
  </code></pre>
  
  <p>I tried to find <code>String_Agg</code> function which is not available in ADF.</p>