If you use union and order, you will always get the error:

"Incorrect usage of UNION and ORDER BY"
$query1 = JFactory::getDbo()->getQuery(true);
$query1->select(array('id', 'title'))->from('#__content')->where('title LIKE ' . $query1->q($query1->e('A', true) . '%', false));
$query2 = JFactory::getDbo()->getQuery(true);
$query2->select(array('id', 'title'))->from('#__content')->where('title LIKE ' . $query1->q($query1->e('B', true) . '%', false));
$query1->union($query2)->order('id DESC');
JFactory::getDbo()->setQuery($query1)->execute();

unionAll doesn't work properly. The string you entered into the unionAll method was never appended to the SQL query

$query1 = JFactory::getDbo()->getQuery(true);
$query1->select(array('id', 'title'))->from('#__content')->where('title LIKE ' . $query1->q($query1->e('A', true) . '%', false));
$query2 = JFactory::getDbo()->getQuery(true);
$query2->select(array('id', 'title'))->from('#__content')->where('title LIKE ' . $query1->q($query1->e('B', true) . '%', false));
echo $query1->unionAll($query2);

Expected result

The code above should output "SELECT id, title FROM #__content WHERE title LIKE 'A%' UNION ALL (SELECT id, title FROM #__content WHERE title LIKE 'B%')".

Actual result

At the moment the output is "SELECT id, title FROM #__content WHERE title LIKE 'A%'".

looks lik this pr is messed up.

yes files changed have nothing in common with the pr description

I've merged two pull requests, but I don't know why. The file to pull is the first one with the id: 22a262d
Do you think I have to close this pull request and open a new one?

yes should be the better move

the bug is solved #10817