How to create a 3rd column based on 2 columns from two tables [inner and outer join] : <ul>
<li>I have a lot of rows in 'table alpha' where some of these rows occurs in 'table beta' as well.</li>
<li>Both row alpha and beta have a date column.

<ul>
<li>However, when i select both date columns the rows from table alpha <strong>that do not occur</strong> in row B will have a null-value assigned to them.</li>
</ul></li>
</ul>

<blockquote>
  <p>My problem is that I want to make a third date-column that will use the dates from table <em>beta</em> <strong>if they are not null</strong>. If they are null, it should use the dates from table alpha.</p>
</blockquote>
