title: Use of Index to Improve Speed of Aggregate functions in select query
body: <p>I need to create a new table with sum aggregates of the measures columns in source table.
  The Source table is very huge.</p>
  
  <p>eg. Source Table</p>
  
  <pre><code>Category | Product | Sales
  A        | P1      | 100 
  B        | P2      | 200
  C        | P3      | 300
  </code></pre>
  
  <p>Query is like : </p>
  
  <pre><code>SELECT Category, 
         Product, 
         SUM(Sales) 
  FROM source_table 
  GROUP BY Category.
  </code></pre>
  
  <p>There is no where condition.</p>
  
  <p>Will indexing help in speeding up the process?<br>
  Any alternate mechanism for speeding the query?</p>