Order By Clause Overridden in Laravel Union Query Construction

Question

I have two queries, $querySelectedItems and $queryRemainingItems, each retrieving a distinct set of items from the 'items' table.

$selecteditemids = [1,3,5,6];

$querySelectedItems = Item::whereIn('id', $selectedItemIds);

$queryRemainingItems = Item::orderBy('activated_at', 'desc')
                    ->whereNotIn('id', $selectedItemIds)

Now to combine both sets of items, I use the union method provided by Laravel's query builder.

$query = $querySelectedItems->union($queryRemainingItems);
$query->get();  //later

However, I encounter an issue where the order by clause specified in $queryRemainingItems is not being applied when using union.

When I observe the resulting items, the combination is correct: $querySelectedItems followed by $queryRemainingItems. But, despite specifying an order by clause in $queryRemainingItems, the order of items from this query is ascending on the activated_at column. Even if I don't explicitly mention or change the order by clause to descending within $queryRemainingItems, the behavior remains the same. It seems that the union method has its own ordering behavior.

Again, without union, if I use merge() that brings correct ordering:

$selectedItems = $querySelectedItems->get();
$remainingItems = $queryRemainingItems->get();
$mergedItems = $selectedItems->merge($remainingItems);

But this approach is not feasible due to project requirements.

How can I ensure that the order by clause specified in $queryRemainingItems is preserved when using union to combine both queries?