如何在 PHP 中的现有数组中插入新元素 - How to insert a new element in an existing array in PHP?

我有一个名为$topic_notes的数组，如下所示：

Array
(
    [0] => Array
        (
            [topic_id] => 214
            [topic_subject_id] => 4
            [topic_notes] => Nice Story
        )
    [1] => Array
        (
            [topic_id] => 215
            [topic_subject_id] => 4
            [topic_notes] => 
        )
    [2] => Array
        (
            [topic_id] => 216
            [topic_subject_id] => 4
            [topic_notes] => 
        )
    [3] => Array
        (
            [topic_id] => 217
            [topic_subject_id] => 4
            [topic_notes] => 
        )
    [4] => Array
        (
            [topic_id] => 218
            [topic_subject_id] => 4
            [topic_notes] => 
        )
    [5] => Array
        (
            [topic_id] => 219
            [topic_subject_id] => 4
            [topic_notes] => 
        )
    [6] => Array
        (
            [topic_id] => 220
            [topic_subject_id] => 4
            [topic_notes] => 
        )
    [7] => Array
        (
            [topic_id] => 221
            [topic_subject_id] => 4
            [topic_notes] => 
        )
    [8] => Array
        (
            [topic_id] => 223
            [topic_subject_id] => 4
            [topic_notes] => 
        )
    [9] => Array
        (
            [topic_id] => 504
            [topic_subject_id] => 4
            [topic_notes] => 
        )
    [10] => Array
        (
            [topic_id] => 225
            [topic_subject_id] => 4
            [topic_notes] => 
        )
)

现在我想在数组$topic_notes中的每个内部数组中创建一个新的键值对，但我无法做到。我尝试过的代码如下：

foreach ($topic_notes as $topic)
  {
    $sql  = "SELECT subject_name FROM ".TBL_SUBJECTS." WHERE subject_id=".$topic['topic_subject_id'];
    $gDb->Query($sql);
    $topic_subject = $gDb->FetchArray(MYSQL_FETCH_SINGLE);
    $subject_name  = $topic_subject['subject_name'];
    $topic_notes['subject'] = $subject_name;     
  }

执行此代码后，我得到以下输出：

Array
    (
        [0] => Array
            (
                [topic_id] => 214
                [topic_subject_id] => 4
                [topic_notes] => Nice Story
            )
        [1] => Array
            (
                [topic_id] => 215
                [topic_subject_id] => 4
                [topic_notes] => 
            )
        [2] => Array
            (
                [topic_id] => 216
                [topic_subject_id] => 4
                [topic_notes] => 
            )
        [3] => Array
            (
                [topic_id] => 217
                [topic_subject_id] => 4
                [topic_notes] => 
            )
        [4] => Array
            (
                [topic_id] => 218
                [topic_subject_id] => 4
                [topic_notes] => 
            )
        [5] => Array
            (
                [topic_id] => 219
                [topic_subject_id] => 4
                [topic_notes] => 
            )
        [6] => Array
            (
                [topic_id] => 220
                [topic_subject_id] => 4
                [topic_notes] => 
            )
        [7] => Array
            (
                [topic_id] => 221
                [topic_subject_id] => 4
                [topic_notes] => 
            )
        [8] => Array
            (
                [topic_id] => 223
                [topic_subject_id] => 4
                [topic_notes] => 
            )
        [9] => Array
            (
                [topic_id] => 504
                [topic_subject_id] => 4
                [topic_notes] => 
            )
        [10] => Array
            (
                [topic_id] => 225
                [topic_subject_id] => 4
                [topic_notes] => 
            )
[subject] => 12 PHYSICS
    )

新的

键值对（即新的数组元素）位于最后的位置。实际上，我希望每个（所有 10 个元素）数组元素中的这个元素。

您需要在

循环中获取索引并在那里设置值，或者只在 for 循环中使用引用。默认情况下，for 循环中的所有项都是其原始数组的副本，因此不会反映对其迭代元素所做的更改。

通过索引

foreach ($topic_notes as $idx => $topic)
{
    // SNIP
    $topic_notes[$idx]['subject'] = $subject_name;     
}

通过参考

foreach ($topic_notes as &$topic)
{
    // SNIP
    $topic['subject'] = $subject_name;     
}

在您的原始示例中，您也没有操纵子数组，而是操作父数组！

您最好在第一个查询（JOIN）中从数据库中获取所有这些内容，但如果这是不可能的，请使用引用，然后更改它：

foreach ($topic_notes as &$topic)
  {
    $sql  = "SELECT subject_name FROM ".TBL_SUBJECTS." WHERE subject_id=".$topic['topic_subject_id'];
    $gDb->Query($sql);
    $topic_subject = $gDb->FetchArray(MYSQL_FETCH_SINGLE);
    $topic['subject'] = $topic_subject['subject_name'];     
  }

试试这个：

foreach ($topic_notes as $index => $topic)
  {
    $sql  = "SELECT subject_name FROM ".TBL_SUBJECTS." WHERE subject_id=".$topic['topic_subject_id'];
    $gDb->Query($sql);
    $topic_subject = $gDb->FetchArray(MYSQL_FETCH_SINGLE);
    $subject_name  = $topic_subject['subject_name'];
    $topic_notes[$index]['subject'] = $subject_name;     
  }

你的意思是：

foreach ($topic_notes as $key => $topic)
  {
    $sql  = "SELECT subject_name FROM ".TBL_SUBJECTS." WHERE subject_id=".$topic['topic_subject_id'];
    $gDb->Query($sql);
    $topic_subject = $gDb->FetchArray(MYSQL_FETCH_SINGLE);
    $subject_name  = $topic_subject['subject_name'];
    $topic_notes[$key]['subject'] = $subject_name;     
  }

旁白：小心字符串连接 - 那里有一个很好的SQL注入错误等待发生......