你可以试试，用这个方法让它变得简单

/**
 * array insert element on position
 * 
 * @link https://vector.cool
 * 
 * @since 1.01.38
 *
 * @param array $original
 * @param mixed $inserted
 * @param int   $position
 * @return array
 */
function array_insert(&$original, $inserted, int $position): array
{
    array_splice($original, $position, 0, array($inserted));
    return $original;
}


$columns = [
    ['name' => '預約項目', 'column' => 'item_name'],
    ['name' => '預約時間', 'column' => 'start_time'],
    ['name' => '預約姓名', 'column' => 'full_name'],
    ['name' => '連絡電話', 'column' => 'phone'],
    ['name' => '建立時間', 'column' => 'create_time']
];
$col = ['name' => '預約帳戶', 'column' => 'user_id'];
$columns = array_insert($columns, $col, 3);
print_r($columns);

打印:

Array
(
    [0] => Array
        (
            [name] => 預約項目
            [column] => item_name
        )
    [1] => Array
        (
            [name] => 預約時間
            [column] => start_time
        )
    [2] => Array
        (
            [name] => 預約姓名
            [column] => full_name
        )
    [3] => Array
        (
            [name] => 報名人數1
            [column] => num_of_people
        )
    [4] => Array
        (
            [name] => 連絡電話
            [column] => phone
        )
    [5] => Array
        (
            [name] => 預約帳戶
            [column] => user_id
        )
    [6] => Array
        (
            [name] => 建立時間
            [column] => create_time
        )
)

function array_insert($array, $position, $insert) {
    if ($position > 0) {
        if ($position == 1) {
            array_unshift($array, array());
        } else {
            $position = $position - 1;
            array_splice($array, $position, 0, array(
                ''
            ));
        }
        $array[$position] = $insert;
    }

    return $array;
}

电话的例子:

$array = array_insert($array, 1, ['123', 'abc']);

在数组开头添加元素的提示:

$a = array('first', 'second');
$a[-1] = 'i am the new first element';

然后:

foreach($a as $aelem)
    echo $a . ' ';
//returns first, second, i am...

but:

for ($i = -1; $i < count($a)-1; $i++)
     echo $a . ' ';
//returns i am as 1st element

function insert(&$arr, $value, $index){       
    $lengh = count($arr);
    if($index<0||$index>$lengh)
        return;

    for($i=$lengh; $i>$index; $i--){
        $arr[$i] = $arr[$i-1];
    }

    $arr[$index] = $value;
}

在做了几天之后，这是我能找到的最简单的解决方案。

$indexnumbertoaddat // this is a variable that points to the index # where you 
want the new array to be inserted

$arrayToAdd = array(array('key' => $value, 'key' => $value)); //this is the new 
 array and it's values that you want to add. //the key here is to write it like 
 array(array('key' =>, since you're adding this array inside another array. This 
 is the point that a lot of answer left out. 

array_splice($originalArray, $indexnumbertoaddatt, 0, $arrayToAdd); //the actual 
splice function. You're doing it to $originalArray, at the index # you define, 
0 means you're just shifting all other index items down 1, and then you add the 
new array. 

这样你就可以插入数组:

function array_insert(&$array, $value, $index)
{
    return $array = array_merge(array_splice($array, max(0, $index - 1)), array($value), $array);
}