PHP usort:使用一个函数按两个键排序

bool usort ( array &$array , callable $cmp_function )

function compare($a, $b) {
    if ($a['key1'] == $b['key1']) {
        return $a['key2'] - $b['key2'];
    }
    return $a['key1'] - $b['key1'];
}

$array = [
    ['key1' => 2, 'key2' => 1],
    ['key1' => 1, 'key2' => 2],
    ['key1' => 2, 'key2' => 2],
    ['key1' => 1, 'key2' => 1]
];

usort($array, 'compare');

print_r($array);

Array
(
    [0] => Array
        (
            [key1] => 1
            [key2] => 1
        )

    [1] => Array
        (
            [key1] => 1
            [key2] => 2
        )

    [2] => Array
        (
            [key1] => 2
            [key2] => 1
        )

    [3] => Array
        (
            [key1] => 2
            [key2] => 2
        )

)