title: Retrieve data from two different table in a single report
body: <p>I have two table Employee and Salary table, salary consists Salary of employee in a field named Salary_employee.
  Second one is Extra Expense, Extra expense consists records related to extra expenses of a company like electricity bills,office maintenance in a field named extra_expense.</p>
  
  <p>(Their is no relationship between these two table).</p>
  
  <p>Finally, I just wanted to show all the expenses of company in a report, for this i need to group both the table. what to use here join or union ??.</p>
  
  <p><img src="https://i.stack.imgur.com/NJpDt.png" alt="">
  <img src="https://i.stack.imgur.com/X2yQH.png" alt=""></p>