1.處理前的陣列：

<?php
$arr1 = array(
    array(
    'id' => 1,
    'user_name'=>'test1'
    ),
    array(
    'id' => 2,
    'user_name'=>'test2'
    ),
    array(
    'id' => 3,
    'user_name'=>'test3'
    )
);
$arr2 = array(
     array(
    'id' => 1,
    'shop_name'=>'shop1'
    ),
    array(
    'id' => 5,
    'shop_name'=>'shop2'
    ),
    array(
    'id' => 3,
    'shop_name'=>'shop3'
    ),
    array(
    'id' => 4,
    'shop_name'=>'shop4'
    )
);
 

2.根據2個數組id相同的一維陣列，將$arr2的shop_name新增到$arr1，將$arr1的user_name新增到$arr2,如果沒有相同的id，shop_name和user_name為空，處理後的陣列：

$new_arr =array(
    array(
    'id' => 1,
    'user_name'=>'test1',
    'shop_name'=>'shop1'
    ),
    array(
    'id' => 2,
    'user_name'=>'test2',
    'shop_name'=>''
    ),
    array(
    'id' => 3,
    'user_name'=>'test3',
    'shop_name'=>'shop3'
    ),
    array(
    'id' => 4,
    'user_name'=>'',
    'shop_name'=>'shop4'
    ),
    array(
    'id' => 5,
    'user_name'=>'',
    'shop_name'=>'shop2'
    ),
);
 

3：處理的過程

$new_arr = array();
foreach ($arr1 as $val) {
    $new_arr[$val['id']] = array('id'=>$val['id'],'shop_name'=>'','user_name'=>$val['user_name']);
}
foreach ($arr2 as $val) {
    if(isset($new_arr[$val['id']])){
        $new_arr[$val['id']]['shop_name'] = $val['shop_name'];
    }else{
        $new_arr[$val['id']] = array('id'=>$val['id'],'shop_name'=>$val['shop_name'],'user_name'=>'',);
    }
}
var_dump(array_values($new_arr));