title: Oracle - Count distinct values of a column
body: <p>I have this table:</p>
  
  <pre><code>Reason|Area_Code|Id
  x         dig     1
  x         dig     2
  y         dig     3
  h         util    4
  x         dig     5
  </code></pre>
  
  <p>I'm trying for a SQL that returns:</p>
  
  <pre><code>Reason|Amount of distinct Reason|Area_code
  x              3                  dig
  y              1                  dig
  h              1                  util
  </code></pre>
  
  <p>I will use this result to plot a chart. I don´t have any idea on how this SQL can be done. Could you help me?</p>