title: Auto generate serial numbers in sql
body: <pre><code>table orders
  +----+--------+------------+
  |s.no|   id   |  ordername |
  +----+--------+------------+
  |  1 |   34   |    name    |      
  +----+--------+------------+
  |  2 |   35   |    name    |        
  +----+--------+------------+
  |  3 |   36   |    name    |        
  +----+--------+------------+
  |  4 |   37   |    name    |        
  +----+--------+------------+
  |  5 |   38   |    name    |       
  +----+--------+------------+
  </code></pre>
  
  <p>write query for auto generate serial numbers and when i delete an order from sql so serial numbers should be as 1234567 in serial_number row and i used order id as auto increment</p>