如何在php中使用此功能

I have this code which bring a single post from my database depend on id

    global $connect;
    $id = $_GET['id'];
    $sql_query="SELECT * FROM `topics` WHERE id = {$id}";
    $result = mysqli_query($connect,$sql_query);
    while ($row = mysqli_fetch_assoc($result)) { ....}

How can i make this as function (My try) :

Function get_single_post($id) {
    global $connect;
    $id = (int)$id;
    $sql_query="SELECT * FROM `topics` WHERE id = {$id}";
    $result = mysqli_query($connect,$sql_query);

    while ($row = mysqli_fetch_assoc($result)) {
        $post[] = $row;
    }
    return $post;
}

to use this function i use this :

get_single_post($_GET['id']);

and when i call something i use : $post['title']; for title as ex

If your id is primary key than you don't need while loop as it will return only one result

modified function

Function get_single_post($id) {
    global $connect;
    $id = (int)$id;
    $sql_query="SELECT * FROM `topics` WHERE id = {$id}";
    $result = mysqli_query($connect,$sql_query);    

    return mysqli_fetch_assoc($result);
}

Remember, a function returns a value, but that value must be assigned to a variable for you to be able to access it.

$post = get_single_post($_GET['id]);

Using the above should now allow you to access the post as you expect.