title: Find missing sequence number in a database
body: <p>Let suppose my database data structure is like that</p>
  
  <pre><code>ShopId   Transaction
  
  001       1.000    
  001       2.000
  001       3.000
  002       1.000
  002       2.000
  002       3.000
  </code></pre>
  
  <p>Now it is might possible that some transaction are missing let suppose</p>
  
  <pre><code>002       4.000
  002       6.000
  </code></pre>
  
  <p>In above table 5.000 transaction of table is missing.</p>
  
  <p><strong>I want to write a query that find the missing sequence number like above in my database.</strong></p>
  
  <p>So my query will return result</p>
  
  <pre><code>   shopid     transaction
     002       5.000
  </code></pre>