title: Select unique records in sqlite
body: <p>Consider a table</p>
  
  <p>results (id, key, value) where key is the Primary key.</p>
  
  <p>Sample data:</p>
  
  <pre><code>id | key      | value
  -----------------------
  abc| source-1 | 20
  abc| source-2 | 30
  abc| source-3 | 2 
  abc| source-4 | 10
  def| source-5 | 1 
  ghi| source-6 | 25
  jkl| source-5 | 13
  </code></pre>
  
  <p>I would like to return only those records which have a single entry for a given id. So output should be</p>
  
  <pre><code>id | key      | value
  ------------------------
  def| source-5 | 1
  ghi| source-6 | 25
  jkl| source-5 | 13
  </code></pre>
  
  <p>Please advise.</p>