如何执行MySQL查询以获取不同订阅中按ID排序的所有行？

Question

A user has subscriptions. They are stored in PHP array. I am trying to get all of the posts that belong to subscriptions ordered by id to display in the news feed. I was trying to get all of them looping throw the array, and after that sorting them by ID. I am wondering if there is an easier way for that, as I decided to use the 'LIMIT' in order to get only the specific amount of posts.

The problem is that now, I get all of the posts, and I need only 10 (for example). I am using PDO, MySQL, PHP. Here is the code I have now:

foreach(subscriptions_arr as $sub) {
    $select = $db->prepare("select * from posts where owner_id = :owner_id");
    $select->bindParam(':owner_id', $sub);
    $select->execute();
    $posts = $select->fetchAll(PDO::FETCH_ASSOC);

    // pushes all of the posts into one multi-array with only 2 levels
    // (instead of 3 as before)
    // to be able to sort it by id, and not by subscriptions
    foreach ($posts as $post) {
        $new_array[] = $post;
    }
}
// sorts by id
usort($new_arr, function($a, $b) {
    return $b['id'] - $a['id'];
});

Now, if I will limit to 10, I will get 10 posts for each of subscriptions, but I need 10 in summary (the latest ones (ordered by ID)).

Answer 1

$select = $db->prepare("select * from posts where owner_id = :owner_id order by id");

这样，记录将以升序排序，请阅读有关ORDER BY子句的信息。

Answer 2

foreach(subscriptions_arr as $sub) {
$select = $db->prepare("select * from posts order by ID DESC group by owner_id LIMIT 10");
$select->execute();
$posts = $select->fetchAll(PDO::FETCH_ASSOC);

// pushes all of the posts into one multi-array with only 2 levels
// (instead of 3 as before)
// to be able to sort it by id, and not by subscriptions
foreach ($posts as $post) {
    $new_array[] = $post;
}
}
// sorts by id
usort($new_arr, function($a, $b) {
return $b['id'] - $a['id'];
});

Answer 3

If you have an array of subscriptions i can suggest to use IN clausole.

$select = $db->prepare("select * from posts where owner_id IN(" . 
implode(',',subscriptions_arr).") ORDER BY owner_id";

$result = $select->execute();