如何在php中结合2个多维数组？

I have 2 multidimensional arrays. I need the union of these arrays. Maybe there is a PHP array function to do this. I tried different ways with array_replace(), array_merge() but I couldn't figure it out. The length array are not fixed. The 2 arrays are:

$a = array(
  array(
    'division'=> 'Dhaka',
    'A'=> 0,
    'B'=> 0,
    'C'=> 0,
    'D'=> 0
  ),
  array(
    'division'=> 'Chittagong',
    'A'=> 0,
    'B'=> 0,
    'C'=> 0,
    'D'=> 0
  ),
  array(
    'division'=> 'Rajshahi',
    'A'=> 0,
    'B'=> 0,
    'C'=> 0,
    'D'=> 0
  ),
  array(
    'division'=> 'Mymensingh',
    'A'=> 0,
    'B'=> 0,
    'C'=> 0,
    'D'=> 0
  )
);
$b = array(
  array("division"=> "Dhaka", "A"=> 5, "B"=> 8),
  array("division"=> "Rajshahi", "A"=> 10, "C"=> 2)
);

The result should be:

$a = array(
      array(
        'division'=> 'Dhaka',
        'A'=> 5, //after union
        'B'=> 8, //after union
        'C'=> 0,
        'D'=> 0
      ),
      array(
        'division'=> 'Chittagong',
        'A'=> 0,
        'B'=> 0,
        'C'=> 0,
        'D'=> 0
      ),
      array(
        'division'=> 'Rajshahi',
        'A'=> 10, //after union
        'B'=> 0, //after union
        'C'=> 2,
        'D'=> 0
      ),
      array(
        'division'=> 'Mymensingh',
        'A'=> 0,
        'B'=> 0,
        'C'=> 0,
        'D'=> 0
      )
    );

Since it's a multi-dimensional array, you need to replace recursively; but you also need identical string indexes. If division is unique then use that:

$a = array_replace_recursive(array_column($a, null, 'division'),
                             array_column($b, null, 'division'));

If you want to get back to integer indexes then:

$a = array_values(array_replace_recursive(array_column($a, null, 'division'),
                                          array_column($b, null, 'division')));