Display list of all values of a custom field
<p>How can I retrieve a list of all values of a specific custom field throughout all posts?</p>

<p>I have a custom field titled "issue_number" and each post is given a numerical value based on the issue to which it belongs. I am trying to display all values of this field to achieve something like this:</p>

<p>-Issue 1<br>
-Issue 2<br>
-Issue 3</p>

<p>Each time a unique value is given to "issue_number", that value will be added to the list.</p>