title: How to write a Kusto query to select only the rows that have unique values in one field
body: <p>Having this input:</p>
  
  <pre><code>let t1 = datatable(id:string, col1:string, col2:string)
  [
      '1', 'col1_1', 'col2_1',
      '2', 'col1_2', 'col2_2',
      '3', 'col1_3', 'col2_3',
      '4', 'col1_4', 'col2_4',
      '1', 'col1_1', 'col2_11',
  ];
  t1 
  | distinct id, col1
  </code></pre>
  
  <p>I need a query that will select only rows with unique values in "id" field. I understand that there are two possible outputs:</p>
  
  <p>Output 1:</p>
  
  <pre><code>'1', 'col1_1', 'col2_1',
  '2', 'col1_2', 'col2_2',
  '3', 'col1_3', 'col2_3',
  '4', 'col1_4', 'col2_4',
  </code></pre>
  
  <p>Output 2:</p>
  
  <pre><code>'2', 'col1_2', 'col2_2',
  '3', 'col1_3', 'col2_3',
  '4', 'col1_4', 'col2_4',
  '1', 'col1_11', 'col2_11',
  </code></pre>