title: Oracle/PLSql Iterate table and index a column
body: <p>I have a table like this</p>
  
  <pre><code>section_id
  =========
     1A
     1A
     1B 
     1B
     1B
     1C
  </code></pre>
  
  <p>and I need to create a numeric column with the index of every element group, like this:</p>
  
  <pre><code> index  section_id
  ======  =========
      1       1A
      2       1A
      1       1B 
      2       1B
      3       1B
      1       1C
  </code></pre>
  
  <p>How can I do this in an Oracle Database?</p>