我无法按日期（特别是按日期）对获得的数据进行分组。
是否可以在sql中或使用pdo fetchall（）执行此操作？
我知道如何在php中以“蹩脚”的方式来实现这一点（循环遍历数据并以我需要的方式处理它以获得所需的结构），但是有没有一种聪明的方法来实现这一点呢？

$sql = "SELECT times.userid AS 'id', times.time AS 'time'
            FROM times
            WHERE ((times.userid) IN ($ids)) AND (times.time BETWEEN #$from# AND #$to#)
            ORDER BY times.time ASC;";

    $stmt = $db->prepare($sql); 
    $stmt->execute();

    $data = $stmt->fetchAll(PDO::FETCH_COLUMN|PDO::FETCH_GROUP);
    return $data;

上述代码的结果是：

[815] => Array
        (
            [0] => 2018-01-01 05:00:00
            [1] => 2018-01-02 08:00:00
            [2] => 2018-01-03 03:00:00
            [3] => 2018-01-03 06:00:00
            [4] => 2018-01-04 03:00:00
            [5] => 2018-01-04 04:00:00
            [6] => 2018-01-05 01:00:00
            [7] => 2018-01-05 03:00:00
            [8] => 2018-01-08 04:00:00
            [9] => 2018-01-09 05:00:00
        )

我想要得到的结果是这样的：

[815] => Array
        (
            [2018-01-01] => Array
                            (
                                [0] => 2018-01-01 05:00:00
                            )
            [2018-01-02] => Array
                            (
                                [0] => 2018-01-02 08:00:00
                            )
            [2018-01-03] => Array
                            (
                                [0] => 2018-01-03 03:00:00
                                [0] => 2018-01-03 06:00:00
                            )
            [2018-01-04] => Array
                            (
                                [0] => 2018-01-04 03:00:00
                                [0] => 2018-01-04 04:00:00
                            )
            [2018-01-05 => Array
                            (
                                [0] => 2018-01-05 01:00:00
                                [0] => 2018-01-05 03:00:00
                            )
            [2018-01-08] => Array
                            (
                                [0] => 2018-01-08 04:00:00
                            )
            [2018-01-09] => Array
                            (
                                [0] => 2018-01-09 05:00:00
                            )
        )