如何执行MySQL查询以获取不同订阅中按ID排序的所有行？

Question

用户已订阅。 它们存储在PHP数组中。 我正在尝试获取所有属于ID订阅的帖子，以显示在新闻Feed中。 我试图让所有这些对象循环抛出该数组，然后按ID对它们进行排序。 我想知道是否有更简单的方法，因为我决定使用“ LIMIT”以仅获取特定数量的帖子。

问题是，现在，我收到了所有帖子，而我只需要10个帖子。 我正在使用PDO，MySQL，PHP。 这是我现在拥有的代码：

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'];
});

现在，如果我限制为10个，则每个订阅将获得10个帖子，但摘要中需要10个帖子（最新的帖子（按ID排序））。

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

如果您有一系列订阅，我建议您使用IN Clausole。

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

$result = $select->execute();