从两个类似的MySQL结果集创建数组时的行为不一致

Question

I am attempting to create multidimensional arrays from data in my database whereby each row would be an array. I have attempted this on two different columns with varying results which I'm not sure why.

First Column Loop :

$db_time_qry = "Select Time from Schedule";
    $db_time_res = mysqli_query($link, $db_time_qry);
    while ($row_c = mysqli_fetch_assoc($db_time_res)) {
        $db_times [] = $row_c['Time'];
    }
    print_r($db_times);

Which returns the following :

Array
(
    [0] => 06:00:00
    [1] => 06:00:00
    [2] => 06:00:00
    [3] => 06:00:00
    [4] => 06:00:00
    [5] => 06:30:00
    [6] => 06:00:00
)

Second Column Loop :

  $qryDay = ("Select Day from Schedule");
    $day_res_ = mysqli_query($link, $qryDay);
    while ($row_day_ = mysqli_fetch_assoc($day_res_)) {
        if (strlen($row_day_['Day'] == 3)) {
            $day_array_ [] = $row_day_['Day'];
        } else {
            $day_array_ [] = explode(',', $row_day_['Day']);
        }
    }
    print_r($day_array_);

Which results into this :

Array
(
    [0] => Array
        (
            [0] => Wed
        )

    [1] => Array
        (
            [0] => Tue
        )

    [2] => Array
        (
            [0] => Tue
        )

    [3] => Array
        (
            [0] => Thu
        )

    [4] => Array
        (
            [0] => Mon
        )

    [5] => Array
        (
            [0] => Sun
            [1] => Mon
            [2] => Tue
        )

    [6] => Array
        (
            [0] => Fri
        )

)

The second loop returns what I want but why are they returning different results whilst using the same loop? Both arrays have been declared outside of the loops like so : $db_times = $day_array_ = [];

Answer 1

In the first one you're adding values to an array

$array[] = value;

This will just add a single value to an array, so it's one-dimensional.

In the second one explode will return an array, so your array contains arrays and is two-dimensional.

If you want an array of arrays, you can use

$array[] = array(value);

So the first one would be

$db_times [] = array($row_c['Time']);

and the second

if (strlen($row_day_['Day'] == 3)) {
    $day_array_ [] = array($row_day_['Day']);
} else {
    $day_array_ [] = explode(',', $row_day_['Day']);
}

You also have an error in your strlen:

strlen($row_day_['Day'] == 3)

This should of course be

strlen($row_day_['Day']) == 3

if you want it to work. Since you're checking strlen of a boolean, it will never match and always go to the explode.