title: get subset of a table in SQL
body: <p>I want to get a subset of a table, here's the example:</p>
  
  <pre><code>1   A
  2   A
  3   B
  4   B
  5   C
  6   D
  7   D
  8   D
  </code></pre>
  
  <p>I want to get the unique record, but with the smallest id:</p>
  
  <pre><code>1   A
  3   B
  5   C
  6   D
  </code></pre>
  
  <p>How can I write the SQL in SQL Server? Thanks!</p>