title: Join two tables with common column names but no related data
body: <p>A picture is worth more than a 1000 words, so here it goes. How could I craft a SQL statement to produce the table below?</p>
  <p><a href="https://i.stack.imgur.com/QlrLK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QlrLK.png" alt="join SQL problem" /></a></p>
  <p>In words, two different tables (Incomes and Expenses) share column names, but the row in each table is unrelated. In this case, an income transaction from a given user is unrelated to an expense transaction, even if it is from the same user.</p>
  <p>I want to join these two tables into a single table such that all columns from both tables appear, but (1) the common table names are &quot;merged&quot; and (2) the unrelatedness of each row of data is preserved such that the distinct table names from one table are NULL when joined to a row from another table.</p>