PHPで2次元配列を1次元配列に変換する方法

array_column(array,column_key,index_key);

$records = [
    [
        'id' => 2135,
        'first_name' => 'John',
        'last_name' => 'Doe',
    ],
    [
        'id' => 3245,
        'first_name' => 'Sally',
        'last_name' => 'Smith',
    ],
    [
        'id' => 5342,
        'first_name' => 'Jane',
        'last_name' => 'Jones',
    ],
    [
        'id' => 5623,
        'first_name' => 'Peter',
        'last_name' => 'Doe',
    ]
];

<?php　　
    $first_names = array_column($records, &#39;first_name&#39;);
　　var_dump($first_names);
?>

$first_names = ['John','Sally','Jane','Peter'];

<?php
　　$first_names = array_column($records, &#39;first_name&#39;，&#39;id&#39;);
　　var_dump($first_names);
?>

$first_names = [2135 =>'John',3245 => 'Sally',5342 => 'Jane',5623 => 'Peter'];