title: add a numeric index in mysql table
body: <p>I have a table with 6 columns having two columns jointly acting as a primary key.</p>
  
  <p>However, I now want to add a numeric index column for each row in the table, so that I can fetch a specific number of rows at a time and keep track to fetch new data every time.</p>
  
  <p>Sorting the current columns would take a lot of time each time as the table is huge. </p>
  
  <p>What can be the best solution?</p>