vertical merge of two columns into a single one
<p>I have three columns as in the below image, and I would like to merge the two columns <code>values1</code> and <code>values2</code> into a single one.  What is the SQL code to do it?</p>

<p><a href="https://i.stack.imgur.com/PXSdO.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PXSdO.png" alt="enter image description here"></a></p>