Pull Request for Issue #15886.

Original report

Hello since i posted this issue at a wrong place i am subitting it as new issue.
I'd love to order articles within a blog-view by unpublish date. Imagine a list of events or similar that should be displayed by their date: next event as first entry, second event as second entry and so on. But as you guys from event organisation know those events are not published in that way: maybe the third event is published as first because alle information is given early.
Here comes my idea: add th option to order by unpublish date: this allowes to create the articles in a chaotic order but show them by their unpubish date (the day after the event).

Steps to reproduce the issue

• create category and a few articles within
• create menu item (category blog)
• order articles by date

Expected result

• select option to order articles by unpublish date

Actual result

• only options are publish_up, modified, created

System information (as much as possible)

• Joomla 3.7.0 and before

Additional comments

maybe it is possible to implement this to root/components/com_content/category/blog.xml around line 270

<field
	name="order_date"
	type="list"
	description="JGLOBAL_ORDERING_DATE_DESC"
	label="JGLOBAL_ORDERING_DATE_LABEL"
>
	<option value="">JGLOBAL_USE_GLOBAL</option>
	<option value="created">JGLOBAL_CREATED</option>
	<option value="modified">JGLOBAL_MODIFIED</option>
	<option value="published">JPUBLISHED</option>
	<option value="unpublished">JUNPUBLISHED</option>
</field>

and then add in root/components/com_content/helpers/query.php around line 170 this

case 'unpublished' :
	$queryDate = ' CASE WHEN a.publish_down = ' . $db->quote($db->getNullDate()) . ' THEN a.created ELSE a.publish_down END ';
	break;

i think in J3.5 this used to work now it doesnt anymore