title: Query to data from two tables having same column but having different data
body: <p>I have two tables one is Registration which has column as reg_id and first_name and other details
  and the other table is activity which also has reg_id  ,first_name and other details with reg_id as common the tables. There can be multiple entries for 1 reg_id in activity table</p>
  
  <p>I want to have query these two tables in such a way ,I want to know all those reg_id which have different first_name in both the tables.</p>
  
  <p>Eg :if </p>
  
  <pre><code>1st table data
  --------------                     
  Reg_id   first_name                               
  1        ashu
  2        &amp;parker
  3        *fzz 
  4        john
  
  
  2nd Table data
  --------------
  Reg_id   first_name
  1        ashu
  2        parker
  3        michel  
  4        john 
  </code></pre>
  
  <p>The output of my query should return 2,3 reg_ids </p>